Monodisperse spherical SiO2 particles were successfully synthesized in 2-propanol-H2O-NH3 system by the microwave hydrothermal method using ammonia as catalyst. To investigate the influences on the size of spherical S...Monodisperse spherical SiO2 particles were successfully synthesized in 2-propanol-H2O-NH3 system by the microwave hydrothermal method using ammonia as catalyst. To investigate the influences on the size of spherical SiO2 particles, factors such as ammonia concentration, reaction temperature, stirring intensity and reactants mol ratio have been studied. The orthogonal experiments were carried out. The as-prepared SiO2 particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA). The results indicated that the size of SiO2 particles increased greatly with the increase in ammonia concentration, temperature and reactants mol ratio, but increased slightly with the increase in stirring intensity. Monodisperse spherical Si02 particles were amorphous with perfect sphere and uniform size. Hydroxyl was detected in SiO2. Kinetic parameters were calculated, and finally the reaction rate equation of dehydrated hydroxyl was obtained.展开更多
This study employed microwave-assisted hydrothermal method to synthesize Ti-MCM-41,which are mesoporous materials with a high surface area and excellent photocatalytic ability. Fourier transform infrared spectroscopy...This study employed microwave-assisted hydrothermal method to synthesize Ti-MCM-41,which are mesoporous materials with a high surface area and excellent photocatalytic ability. Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), and ultraviolet–visible spectroscopy(UV–Vis) were employed. The XRD findings showed that Ti-MCM-41 exhibited a peak at 2θ of 2.2°, which was attributed to the hexagonal MCM-41 structure. The BET(Brunauer–Emmett–Teller) results agreed with the TEM findings that Ti-MCM-41 has a pore size of about 3–5 nm and a high surface area of 883 m-2/g. FTIR results illustrated the existence of Si–O–Si and Si–O–Ti bonds in Ti-MCM-41. The appearance of Ti2 p peaks in the XPS results confirmed the FTIR findings that the Ti was successfully doped into the MCM-41 structure. Zeta(ζ)-potential results indicated that the iso-electric point(IEP) of Ti-MCM-41 was at about pH 3.02. In this study, the photocatalytic degradation of oxytetracycline(OTC) at different pH was investigated under Hg lamp irradiation(wavelength 365 nm). The rate constant(K′obs) for OTC degradation was 0.012 min-1at pH 3. Furthermore, TOC(total organic carbon) and high resolution LC–MS(liquid chromatography–mass spectrometry) analyses were conducted to elucidate the possible intermediate products and degradation pathway for OTC. The TOC removal efficiency of OTC degradation was 87.0%, 74.4% and 50.9% at pH 3, 7 and 10, respectively. LC–MS analysis results showed that the degradation products from OTC resulted from the removal of functional groups from the OTC ring.展开更多
In this research, cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O) with Ce3+-to-Mo6+ molar ratio of 2:3 were dissolved in 40 ml different ...In this research, cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O) with Ce3+-to-Mo6+ molar ratio of 2:3 were dissolved in 40 ml different solvents of deionized (DI) water, polyethylene glycol (PEG) and ethylene glycol (EG) to form different solutions which were followed by adjusting pH from the traditional values to 7.0 and 10.0 with 1 mol.L-1 sodium hydroxide (NaOH). Subsequently, the solutions were processed by 270-W microwave-hydrother- mal/solvothermal method. Phase, morphology, vibrational modes and photonic properties were fully characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectrophotometry, ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy. The as-synthe-sized products were pure cerium molybdenum oxide (Ce2(MoO4)3) of nanoparticles clustered together as nano- plates in DI water and PEG solvents, and of spindle-like nanoparticles in EG solvent, including the presence of Ce-O-H mode and MoO4 units. The results show that direct energy gaps of the first two have the same value of 2.30 eV, and that of the last is 2.80 eV, including their blue emission at the same wavelength of 488 nm.展开更多
Scandia stabilized zirconia powder (ScSZ) was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction (XRD), Raman, scann...Scandia stabilized zirconia powder (ScSZ) was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Weakly agglomerated and well crystallized ScSZ powder was prepared by microwave-heating to 150 ℃ and 2.5 h. The structure of the ScSZ powder changed from a tetragonal to a cubic phase, and accordingly, the powder conductivity was increased from 90.55 to 120.56 ms/cm by the introduction of the mineralizer solutions (KOH+K2CO3) during the microwave-hydrothermal processing.展开更多
Anatase titania nanoparticles with an average size of about 14 nm were synthesized by microwave solvothermal method from TiCI4 and ethanol as a precursor and solvent respectively. The shapes of as prepared samples wer...Anatase titania nanoparticles with an average size of about 14 nm were synthesized by microwave solvothermal method from TiCI4 and ethanol as a precursor and solvent respectively. The shapes of as prepared samples were modified by microwave hydrothermal treatment in strongly alkaline medium at 100℃ for 2 h, the agglomerate particles can be converted to the nanorods then to flower-like sphere. The structure, morphology and optical properties of as-prepared powders were investigated by X-ray diffraction, scanning electron microscopy and UV- vis absorption spectroscopy, the quality of the samples was examined by IR absorption spectroscopy and room temperature photoluminescence (PL). The results showed that the synthesized Ti02 revealed the formation of the nanorods and the flower-like shape of titania after post treatment in 5 mol/L and 10 mol/L NaOH solution, respectively. IR absorption spectra showed that the as-prepared TiO2 nanocrystals were highly pure and strongly surface hydrated, The photoluminescence measurement showed that five main emission peaks appeared in UV, violet, blue and green regions.展开更多
Ion exchanging is one of the characteristics of the zeolites. Zeolites have octahedral and tetrahedral holes to trap ions and molecules. They also can exchange many ions in solution because of the size of the attendan...Ion exchanging is one of the characteristics of the zeolites. Zeolites have octahedral and tetrahedral holes to trap ions and molecules. They also can exchange many ions in solution because of the size of the attendant ions. As a matter of fact, the property of the ion-exchanged zeolites depends on the ligands involved in the ion exchanging solutions. Ion exchanged zeolites are used as catalyst for studying the anodic oxidation of methanol in an acidic medium to investigate their suitability for use in direct methanol fuel cells (DMFCs). Some of the zeolites that have exchanged ions are shown to have redox and catalytic properties [1-3]. As an example A. Itadani et al., have reported the preparation of copper ion exchanged ZSM-5 for calorimetric study of N2 adsorption on Cu-ZSM-5 zeolite [4]. In another study, A. Ribera et al. have reported the characterization of redox properties and application of Fe-ZSM-5 catalysts [5]. In this research we prepared silicate solutions by dissolving silica in sodium hydroxide. Aluminosilicate solutions with different Al/Si ratios were prepared by mixing appropriate quantities of sodium silicate solutions with freshly prepared sodium aluminate solutions and the NaA zeolites were made by hydrothermal method. Then, their XRD patterns and IR spectra were also considered. Obviously, those zeolites which have Al-OH and Si-OH groups can lose their protons in basic solutions. In this way zeolites can adsorb many ions with positive charge. We investigated ion exchange property of Fe3+, Cu2+, Ni2+ and Hg2+ in systems with pH equals to 2, 4, 6 and 8. We found that the aluminosilicate with Si/Al = 1, has greatest exchange capacity for all of the ions studied in this work.展开更多
A facile one-step hydrothermal method has been reported to synthesize theα-Fe_(2)O_(3)nanosheet arrays with the preferred orientation along the[104]direction on the ITO substrate.Theα-Fe_(2)O_(3)nanosheet arrays-bas...A facile one-step hydrothermal method has been reported to synthesize theα-Fe_(2)O_(3)nanosheet arrays with the preferred orientation along the[104]direction on the ITO substrate.Theα-Fe_(2)O_(3)nanosheet arrays-based W/α-Fe_(2)O_(3)/ITO memristor has been achieved by depositing the circular W top electrodes on theα-Fe_(2)O_(3)nanosheet arrays.The as-prepared W/α-Fe_(2)O_(3)/ITO memristor shows a reliable nonvolatile bipolar resistive switching behavior with the high resistance ratio of about 103at the reading voltage of 0.1 V,good resistance retention over 10~3s,ultralow set voltage of-0.6 V and reset voltage of 0.7 V,and good durability.In addition,the tunneling conduction mechanism modified by the oxygen vacancies has been proposed and suggested to be responsible for the nonvolatile resistive switching behavior of the as-prepared W/α-Fe_(2)O_(3)/ITO memristor.This work demonstrates that the as-preparedα-Fe_(2)O_(3)nanosheet arrays-based W/α-Fe_(2)O_(3)/ITO memristor would be a promising candidate for further ultralow power nonvolatile memory applications.展开更多
In this work,microwave treatment was introduced to a hydrothermal treatment process to degrade PCDD/Fs(Polychlorinated dibenzo-p-dioxins and dibenzofurans)in municipal solid waste incineration(MSWI)fly ash.Three proce...In this work,microwave treatment was introduced to a hydrothermal treatment process to degrade PCDD/Fs(Polychlorinated dibenzo-p-dioxins and dibenzofurans)in municipal solid waste incineration(MSWI)fly ash.Three process additives(NaOH,Na2 HPO4,H2 O),temperatures(150℃,185℃,220℃)and reaction times(1 h,2 h,3 h)were investigated to identify their effect on the disposal of fly ash samples through orthogonal experiments.High-resolution gas chromatography–mass spectrometry(HRGC/MS)was applied to determine the PCDD/F concentrations in MSWI fly ash.The experimental results revealed that 83.7%of total PCDD/Fs was degraded.Reaction temperature was the most important factor for the degradation of the total PCDD/Fs.Both direct destruction and chlorination reactions(the chlorination degree of PCDFs increased)took part in the degradation of PCDD/Fs in fly ash,which was a new discovery.Several PCDD/F indexes determined by the concentration of indicative congeners were found to quantitatively characterize the dioxin toxicity of the fly ash.Furthermore,heavy metals in the fly ash sample were solidified using microwave-assisted hydrothermal treatment,which provided an experimental basis for the simultaneous disposal of dioxins and heavy metals.Thus,the microwave-assisted hydrothermal process should be considered for the future disposal of MSWI fly ash.展开更多
Two-step synthesis of Y2O3:Eu nanostructures was performed.It includes microwave driven hydrothermal and calcination stages.Performed route results in crystallization of Y4O(OH)g(NO3):Eu crystals initially,then Y2O3:E...Two-step synthesis of Y2O3:Eu nanostructures was performed.It includes microwave driven hydrothermal and calcination stages.Performed route results in crystallization of Y4O(OH)g(NO3):Eu crystals initially,then Y2O3:Eu crystals after calcination.Arranged Eu contents in relation to overall cation quantity were set to 2 mol%,10 mol%and 20 mol%.Varying europium concentrations influence habit of obtained Y4O(OH)g(NO3):Eu crystals from needle-like to plate-like and as a result,also shapes of final Y2O3:Eu nanostructures.Additionally,certain amount of Eu2+ions was detected in as-grown material using laser spectroscopy and decay kinetics measurements.Obtained material was calcined at 1200°C in the air,which results in oxidation of Eu2+ions and crystallization of small number of cubic EU2 O3 nanocrystals.Characterization of obtained materials was performed using XRD,SEM,TEM,EDX,CL,Raman and photoluminescence spectroscopy.展开更多
In this paper,the Pt/SnO2 nanostructures were prepared via a facile one-step microwave assisted hydrothermal route.The structure of the introduced Pt/SnO2 and its gas-sensing properties toward CO were investigated.The...In this paper,the Pt/SnO2 nanostructures were prepared via a facile one-step microwave assisted hydrothermal route.The structure of the introduced Pt/SnO2 and its gas-sensing properties toward CO were investigated.The results from the TEM test reveal that Pt grows on the SnO2 nanostructure,which was not found for bulk in this situ method,constructing Pt/SnO2.The results indicated that the sensor using 3.0 wt%Pt/SnO2 to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt%and 4.5 wt%Pt/SnO2 at 225℃.The response time of 3.0 wt%sensor is 16 s to 100 ppm CO at225℃.Such enhanced gas sensing performances could be attributed to the chemical and electrical factors.In view of chemical factors,the presence of Pt facilitates the surface reaction,which will improve the gas sensing properties.With respect to the electrical factors,the Pt/SnO2 plays roles in increasing the sensor’s response due to its characteristic configuration.In addition,the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.展开更多
In order to improve the quality of 3D printed raspberry preserves after post-processing,microwave ovens combining infrared and microwave methods were utilized.The effects of infrared heating temperature,infrared heati...In order to improve the quality of 3D printed raspberry preserves after post-processing,microwave ovens combining infrared and microwave methods were utilized.The effects of infrared heating temperature,infrared heating time,microwave power,microwave heating time on the center temperature,moisture content,the chroma(C*),the total color difference(ΔE*),shape fidelity,hardness,and the total anthocyanin content of 3D printed raspberry preserves were analyzed by response surface method(RSM).The results showed that under combining with the two methods,infrared heating improved the fidelity and quality degradation of printed products,while microwave heating enhanced the efficiency of infrared heating.Infrared-microwave combination cooking could maintain relatively stable color appearance and shape of 3D printed raspberry preserves.The AHP–CRITIC hybrid weighting method combined with the response surface test to determine the comprehensive weights of the evaluation indicators optimized the process parameters,and the optimal process parameters were obtained:infrared heating temperature of 190℃,infrared heating time of 10 min and 30 s,microwave power of 300 W,and microwave heating time of 2 min and 6 s.The 3D printed raspberry cooking methods obtained under the optimal conditions seldom had color variation,porous structure,uniform texture,and high shape fidelity,which retained the characteristics of personalized manufacturing by 3D printing.This study could provide a reference for the postprocessing and quality control of 3D cooking methods.展开更多
This paper adopted the hydrothermal method to prepare tungsten oxide(WO_(3))nanorod films and studied the effects of precursor solution concentration(0.02,0.03,0.06 mol/L peroxytungstic acid)and annealing temperature(...This paper adopted the hydrothermal method to prepare tungsten oxide(WO_(3))nanorod films and studied the effects of precursor solution concentration(0.02,0.03,0.06 mol/L peroxytungstic acid)and annealing temperature(200,300,400℃)on their electrochromic properties.The microstructure characterization of WO_(3) films were performed using scanning electron microscope(SEM),X-ray diffraction(XRD),and transmission electron microscope(TEM),and their electrochromic properties were tested by combining an electrochemical workstation with an ultraviolet-visible spectrophotometer.The results showed that the precursor solution concentration directly affected the thickness(290,560,990 nm)and microstructure of WO_(3) films,significantly impacting their electrochromic properties.However,the annealing temperature had a negligible effect.As the precursor solution concentration increased,the optical modulation of WO_(3) films gradually decreased,reaching 51.1%,43.8%,and 35.1%,respectively.The switching time first increased and then stabilized,with coloring times of 7.3,7.7,and 7.7 s,respectively,and bleaching times of 3.8,6.5,and 6.5 s,respectively.The coloration efficiency gradually increased but the increase was relatively small,reaching 41.8,44.4,and 44.8 cm^(2)/C,respectively.Moreover,the cycling stability of WO_(3) films was poor,with the ratios of the final value of optical modulation to the initial value 0.33,0.26,and 0.34,respectively.Additionally,there were bigger differences in the bleached state transmittance,while the colored state transmittance showed smaller variations.However,the former has better cycling stability than the latter.In summary,to obtain better electrochromic properties,the thickness of WO_(3) films should not exceed 290 nm.展开更多
It was focused on the applications and developments of microwave hydrothermal synthesis piezoelectric ceramic powder. The microwave hydrothermal vessel was designed and manufactured. The microwave hydrothermal synthes...It was focused on the applications and developments of microwave hydrothermal synthesis piezoelectric ceramic powder. The microwave hydrothermal vessel was designed and manufactured. The microwave hydrothermal synthesis system was established and the PZT piezoelectric ceramic powder was synthesized. XRD and TEM have been used to characterize the products in detail. The diameter of the PZT powder particle is from 40 to 60 nm.展开更多
In this study, SnNb_2O_6 and Sn_2Nb_2O_7 nanosheets are synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. The SnNb_2O_6 electrode exhibits hi...In this study, SnNb_2O_6 and Sn_2Nb_2O_7 nanosheets are synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. The SnNb_2O_6 electrode exhibits high reversible capacity and excellent cycling stability(498 mAh/g at 0.1 A/g after 100 cycles),which is superior to that of Sn_2Nb_2O_7 electrode(173 mAh/g at 0.1 A/g after 100 cycles). Even increasing the current density to 2.0 A/g, the SnNb_2O_6 electrode still delivers a reversible capacity up to 306 mAh/g.The rate performance of the SnNb_2O_6 electrode is also better than that of Sn_2 Nb_2O_7 electrode at different current densities from 0.1 A/g to 2.0 A/g. The enhanced electrochemical performance of SnNb_2O_6 nanosheets can be attributed to the unique layered structure, which is conducive to the diffusion of the lithium ions and the migration of electrons during discharge/charge.展开更多
A large surface area with high active site exposure is desired for the nano-scaled electrocatalysts fabrica-tion.Herein,taking NiMoO_(4)nanorods for example,we demonstrated the advantages of the microwave-assisted hyd...A large surface area with high active site exposure is desired for the nano-scaled electrocatalysts fabrica-tion.Herein,taking NiMoO_(4)nanorods for example,we demonstrated the advantages of the microwave-assisted hydrothermal synthesis method compared to the traditional hydrothermal approaches.Both monoclinic structured NiMoO_(4)in the nanorods morphology are found for these samples but it is more time-saving and efficient in the Ni-Mo synergism for the catalyst obtained by microwave-assisted hydrothermal syntheses method.When evaluated for urea oxidation,the current density can reach 130.79 mA/cm^(2)at 1.54 V,about 2.4 times higher than that of the counterpart catalyst(54.08 mA/cm^(2)).Moreover,largely improved catalytic stability,catalytic kinetics and rapid charge transfer ability are found on the catalyst obtained by the microwave-assisted approach.The high catalytic performance can be at-tributed to the high surface area and active site exposure of NiMoO_(4)nanorods formed by microwave irradiation.Considering the less time,facile synthesis condition and efficient components synergism,the microwave-assisted hydrothermal synthesis method might work better for the nanostructure electrocata-lysts fabrication.展开更多
In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,...In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S)in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS2 is a candidate for a practical microwave absorbent.展开更多
Microwave-induced nitrogen-doped titanate nanotubes(NTNTs) were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared...Microwave-induced nitrogen-doped titanate nanotubes(NTNTs) were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR), Zeta potential analysis,specific surface area(SBET), and UV-Visible spectroscopy. TEM results indicate that NTNTs retain a tubular structure with a crystalline multiwall and have a length of several hundred nanometers after nitrogen doping. XRD findings demonstrate that the crystalline structure of NTNTs was dominated by anatase, which is favored for photocatalytic application. The Ti-O-N linkage observed in the XPS N 1s spectrum is mainly responsible for narrowing the band gap and eventually enhancing the visible light photoactivity. FT-IR results demonstrated the existence of H3O+, which could be excited by photo-generated holes to form hydroxyl radicals and degrade environmental pollutants. After sintering at 350°C, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which indicates N atom doping into the nanotubes. Photocatalytic degradation of Rhodamine B(RhB) via NTNTs show good efficiency, with pseudo first-order kinetic model rate constants of 3.7 × 10-3, 2.4 × 10-3and 8.0 × 10-4sec-1at pH 3, 7, and 11, respectively.展开更多
Effects of La, N, and P doping on the structural, electronic and optical properties of TiO_2 synthesized from TiCl_4 hydrolysis via a microwave-hydrothermal process were investigated by X-ray diffraction, transmission...Effects of La, N, and P doping on the structural, electronic and optical properties of TiO_2 synthesized from TiCl_4 hydrolysis via a microwave-hydrothermal process were investigated by X-ray diffraction, transmission electron microscopy, N_2 adsorption-desorption isotherm, X-ray photoelectron spectroscopy, electron paramagnetic resonance, UV-vis absorbance spectroscopy, photoelectrochemical measurements, and photoluminescence spectroscopy. The results showed that the presence of La in the tri-doped TiO_2 played a predominant role in inhibiting the recombination of the photogenerated electrons and holes. The existence of the substitutional N, interstitial N, and oxygen vacancies in TiO_2 lattices led to the band gap narrowing. It was P-doping rather than La or N doping that played a key role in inhibiting both anatase-to-rutile phase transformation and crystal growth, in stabilizing the mesoporous textural properties, and in increasing the content of surface bridging hydroxyl. Moreover, the tri-doping significantly enhanced the surface Ti^(4+)-O^(2-)-Ti^(4+)-O^(-·) species. All above-mentioned factors cooperated to result in the enhanced photoactivity of the tri-doped TiO_2. As a result, it exhibited the highest photoactivity towards the degradation of 4-chlorophenol(4-CP) under visible-light irradiation among all samples, which was much superior to commercial P25 TiO_2.展开更多
We have developed a microwave-assisted hydrothermal method,where both microwave and hydrothermal techniques are utilized to synthesize CdTe nanocrystals with high quality in less than 55 s.Among the known preparation ...We have developed a microwave-assisted hydrothermal method,where both microwave and hydrothermal techniques are utilized to synthesize CdTe nanocrystals with high quality in less than 55 s.Among the known preparation methods,the monodisperse CdTe nanocrystals showing narrow emission spectra,widest scope of emission peak(from 500 nm to 822 nm) and high quantum yield(up to 80%) were synthesized by this route.The quantum yield of CdTe with near-infrared emission(800 nm) is up to 10%,which is better than that of InAs(0.5%―2%) synthesized in organic phase.Moreover,we detected the latent fingerprints on aluminum,plastic,glass and papers by prepared CdTe nanocrystals,and photoluminescence fingerprints images were taken with a digital camera.Then the images would transmitt into fingerprint detection system of computer to identify the criminals in suit.展开更多
Bi(0.76)Sb(1.24)S3 nanocrystals were synthesized by a rapid microwave-assisted hydrothermal method using bismuth nitrate, antimony pentoxide and thioacetamide as starting materials and characterized by X-ray diffr...Bi(0.76)Sb(1.24)S3 nanocrystals were synthesized by a rapid microwave-assisted hydrothermal method using bismuth nitrate, antimony pentoxide and thioacetamide as starting materials and characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and UV-vis diffuse reflectance spectroscopy(DRS). The effects of the synthetic condition on the product composition were investigated. The photocatalytic activities of Bi(0.76)Sb(1.24)S3 nanocrystals for the degradation of methyl orange and p-hydroxyazobenzene under visible light irradiation were evaluated. Bi(0.76)Sb(1.24)S3 exhibited good and stable visible light photocatalytic activity.展开更多
基金supported by the National Basic Research Program of China (Grant No.2007CB613603)
文摘Monodisperse spherical SiO2 particles were successfully synthesized in 2-propanol-H2O-NH3 system by the microwave hydrothermal method using ammonia as catalyst. To investigate the influences on the size of spherical SiO2 particles, factors such as ammonia concentration, reaction temperature, stirring intensity and reactants mol ratio have been studied. The orthogonal experiments were carried out. The as-prepared SiO2 particles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis (DTA). The results indicated that the size of SiO2 particles increased greatly with the increase in ammonia concentration, temperature and reactants mol ratio, but increased slightly with the increase in stirring intensity. Monodisperse spherical Si02 particles were amorphous with perfect sphere and uniform size. Hydroxyl was detected in SiO2. Kinetic parameters were calculated, and finally the reaction rate equation of dehydrated hydroxyl was obtained.
基金financial support provided by the Tunghai University Global Research and Education on Environment and Society (No. 103GREEnS 005-2)
文摘This study employed microwave-assisted hydrothermal method to synthesize Ti-MCM-41,which are mesoporous materials with a high surface area and excellent photocatalytic ability. Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM), and ultraviolet–visible spectroscopy(UV–Vis) were employed. The XRD findings showed that Ti-MCM-41 exhibited a peak at 2θ of 2.2°, which was attributed to the hexagonal MCM-41 structure. The BET(Brunauer–Emmett–Teller) results agreed with the TEM findings that Ti-MCM-41 has a pore size of about 3–5 nm and a high surface area of 883 m-2/g. FTIR results illustrated the existence of Si–O–Si and Si–O–Ti bonds in Ti-MCM-41. The appearance of Ti2 p peaks in the XPS results confirmed the FTIR findings that the Ti was successfully doped into the MCM-41 structure. Zeta(ζ)-potential results indicated that the iso-electric point(IEP) of Ti-MCM-41 was at about pH 3.02. In this study, the photocatalytic degradation of oxytetracycline(OTC) at different pH was investigated under Hg lamp irradiation(wavelength 365 nm). The rate constant(K′obs) for OTC degradation was 0.012 min-1at pH 3. Furthermore, TOC(total organic carbon) and high resolution LC–MS(liquid chromatography–mass spectrometry) analyses were conducted to elucidate the possible intermediate products and degradation pathway for OTC. The TOC removal efficiency of OTC degradation was 87.0%, 74.4% and 50.9% at pH 3, 7 and 10, respectively. LC–MS analysis results showed that the degradation products from OTC resulted from the removal of functional groups from the OTC ring.
基金financially supported by Thailand's Office of the Higher Education Commission through the National Research University Project for Chiang Mai University
文摘In this research, cerium (III) nitrate hexahydrate (Ce(NO3)3·6H2O) and ammonium molybdate tetrahydrate ((NH4)6Mo7O24·4H2O) with Ce3+-to-Mo6+ molar ratio of 2:3 were dissolved in 40 ml different solvents of deionized (DI) water, polyethylene glycol (PEG) and ethylene glycol (EG) to form different solutions which were followed by adjusting pH from the traditional values to 7.0 and 10.0 with 1 mol.L-1 sodium hydroxide (NaOH). Subsequently, the solutions were processed by 270-W microwave-hydrother- mal/solvothermal method. Phase, morphology, vibrational modes and photonic properties were fully characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman spectrophotometry, ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy. The as-synthe-sized products were pure cerium molybdenum oxide (Ce2(MoO4)3) of nanoparticles clustered together as nano- plates in DI water and PEG solvents, and of spindle-like nanoparticles in EG solvent, including the presence of Ce-O-H mode and MoO4 units. The results show that direct energy gaps of the first two have the same value of 2.30 eV, and that of the last is 2.80 eV, including their blue emission at the same wavelength of 488 nm.
基金Project supported by National Science and Technology Support Project of China(2012BAB10B11)Rare-earth Adjustment Up grade Projects of Ministry of Industry and Information Technology of China
文摘Scandia stabilized zirconia powder (ScSZ) was first synthesized by a microwave-hydrothermal method. The crystalline and aggregated particle sizes were investigated by means of X-ray diffraction (XRD), Raman, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Weakly agglomerated and well crystallized ScSZ powder was prepared by microwave-heating to 150 ℃ and 2.5 h. The structure of the ScSZ powder changed from a tetragonal to a cubic phase, and accordingly, the powder conductivity was increased from 90.55 to 120.56 ms/cm by the introduction of the mineralizer solutions (KOH+K2CO3) during the microwave-hydrothermal processing.
文摘Anatase titania nanoparticles with an average size of about 14 nm were synthesized by microwave solvothermal method from TiCI4 and ethanol as a precursor and solvent respectively. The shapes of as prepared samples were modified by microwave hydrothermal treatment in strongly alkaline medium at 100℃ for 2 h, the agglomerate particles can be converted to the nanorods then to flower-like sphere. The structure, morphology and optical properties of as-prepared powders were investigated by X-ray diffraction, scanning electron microscopy and UV- vis absorption spectroscopy, the quality of the samples was examined by IR absorption spectroscopy and room temperature photoluminescence (PL). The results showed that the synthesized Ti02 revealed the formation of the nanorods and the flower-like shape of titania after post treatment in 5 mol/L and 10 mol/L NaOH solution, respectively. IR absorption spectra showed that the as-prepared TiO2 nanocrystals were highly pure and strongly surface hydrated, The photoluminescence measurement showed that five main emission peaks appeared in UV, violet, blue and green regions.
文摘Ion exchanging is one of the characteristics of the zeolites. Zeolites have octahedral and tetrahedral holes to trap ions and molecules. They also can exchange many ions in solution because of the size of the attendant ions. As a matter of fact, the property of the ion-exchanged zeolites depends on the ligands involved in the ion exchanging solutions. Ion exchanged zeolites are used as catalyst for studying the anodic oxidation of methanol in an acidic medium to investigate their suitability for use in direct methanol fuel cells (DMFCs). Some of the zeolites that have exchanged ions are shown to have redox and catalytic properties [1-3]. As an example A. Itadani et al., have reported the preparation of copper ion exchanged ZSM-5 for calorimetric study of N2 adsorption on Cu-ZSM-5 zeolite [4]. In another study, A. Ribera et al. have reported the characterization of redox properties and application of Fe-ZSM-5 catalysts [5]. In this research we prepared silicate solutions by dissolving silica in sodium hydroxide. Aluminosilicate solutions with different Al/Si ratios were prepared by mixing appropriate quantities of sodium silicate solutions with freshly prepared sodium aluminate solutions and the NaA zeolites were made by hydrothermal method. Then, their XRD patterns and IR spectra were also considered. Obviously, those zeolites which have Al-OH and Si-OH groups can lose their protons in basic solutions. In this way zeolites can adsorb many ions with positive charge. We investigated ion exchange property of Fe3+, Cu2+, Ni2+ and Hg2+ in systems with pH equals to 2, 4, 6 and 8. We found that the aluminosilicate with Si/Al = 1, has greatest exchange capacity for all of the ions studied in this work.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62341305 and 22269002)the Natural Science Foundation of Guangxi Zhuang Autonomous Region,China(Grant No.2024GXNSFFA010007)+2 种基金the Science and Technology Project of Guangxi Zhuang Autonomous Region,China(Grant No.AD19110038)the Key Laboratory of AI and Information Processing,Education Department of Guangxi Zhuang Autonomous Region(Grant No.2024GXZDSY015)the Innovation Project of Guangxi University of Science and Technology Graduate Education(Grant No.GKYC202408)。
文摘A facile one-step hydrothermal method has been reported to synthesize theα-Fe_(2)O_(3)nanosheet arrays with the preferred orientation along the[104]direction on the ITO substrate.Theα-Fe_(2)O_(3)nanosheet arrays-based W/α-Fe_(2)O_(3)/ITO memristor has been achieved by depositing the circular W top electrodes on theα-Fe_(2)O_(3)nanosheet arrays.The as-prepared W/α-Fe_(2)O_(3)/ITO memristor shows a reliable nonvolatile bipolar resistive switching behavior with the high resistance ratio of about 103at the reading voltage of 0.1 V,good resistance retention over 10~3s,ultralow set voltage of-0.6 V and reset voltage of 0.7 V,and good durability.In addition,the tunneling conduction mechanism modified by the oxygen vacancies has been proposed and suggested to be responsible for the nonvolatile resistive switching behavior of the as-prepared W/α-Fe_(2)O_(3)/ITO memristor.This work demonstrates that the as-preparedα-Fe_(2)O_(3)nanosheet arrays-based W/α-Fe_(2)O_(3)/ITO memristor would be a promising candidate for further ultralow power nonvolatile memory applications.
基金Supported by the Innovative Research Groups of the National Natural Science Foundation of China(51621005)the National Natural Science Foundation of China(51676172)
文摘In this work,microwave treatment was introduced to a hydrothermal treatment process to degrade PCDD/Fs(Polychlorinated dibenzo-p-dioxins and dibenzofurans)in municipal solid waste incineration(MSWI)fly ash.Three process additives(NaOH,Na2 HPO4,H2 O),temperatures(150℃,185℃,220℃)and reaction times(1 h,2 h,3 h)were investigated to identify their effect on the disposal of fly ash samples through orthogonal experiments.High-resolution gas chromatography–mass spectrometry(HRGC/MS)was applied to determine the PCDD/F concentrations in MSWI fly ash.The experimental results revealed that 83.7%of total PCDD/Fs was degraded.Reaction temperature was the most important factor for the degradation of the total PCDD/Fs.Both direct destruction and chlorination reactions(the chlorination degree of PCDFs increased)took part in the degradation of PCDD/Fs in fly ash,which was a new discovery.Several PCDD/F indexes determined by the concentration of indicative congeners were found to quantitatively characterize the dioxin toxicity of the fly ash.Furthermore,heavy metals in the fly ash sample were solidified using microwave-assisted hydrothermal treatment,which provided an experimental basis for the simultaneous disposal of dioxins and heavy metals.Thus,the microwave-assisted hydrothermal process should be considered for the future disposal of MSWI fly ash.
基金Project supported by National Science Centre(2012/05/E/NZ4/02994,2012/06/A/ST7/00398)
文摘Two-step synthesis of Y2O3:Eu nanostructures was performed.It includes microwave driven hydrothermal and calcination stages.Performed route results in crystallization of Y4O(OH)g(NO3):Eu crystals initially,then Y2O3:Eu crystals after calcination.Arranged Eu contents in relation to overall cation quantity were set to 2 mol%,10 mol%and 20 mol%.Varying europium concentrations influence habit of obtained Y4O(OH)g(NO3):Eu crystals from needle-like to plate-like and as a result,also shapes of final Y2O3:Eu nanostructures.Additionally,certain amount of Eu2+ions was detected in as-grown material using laser spectroscopy and decay kinetics measurements.Obtained material was calcined at 1200°C in the air,which results in oxidation of Eu2+ions and crystallization of small number of cubic EU2 O3 nanocrystals.Characterization of obtained materials was performed using XRD,SEM,TEM,EDX,CL,Raman and photoluminescence spectroscopy.
基金supported by the National Natural Science Foundation of China (No.61803172)the Start-up Research Foundation of Hainan University (No.KYQD(ZR)1910)。
文摘In this paper,the Pt/SnO2 nanostructures were prepared via a facile one-step microwave assisted hydrothermal route.The structure of the introduced Pt/SnO2 and its gas-sensing properties toward CO were investigated.The results from the TEM test reveal that Pt grows on the SnO2 nanostructure,which was not found for bulk in this situ method,constructing Pt/SnO2.The results indicated that the sensor using 3.0 wt%Pt/SnO2 to 100 ppm carbon monoxide performed a superior sensing properties compared to 1.5 wt%and 4.5 wt%Pt/SnO2 at 225℃.The response time of 3.0 wt%sensor is 16 s to 100 ppm CO at225℃.Such enhanced gas sensing performances could be attributed to the chemical and electrical factors.In view of chemical factors,the presence of Pt facilitates the surface reaction,which will improve the gas sensing properties.With respect to the electrical factors,the Pt/SnO2 plays roles in increasing the sensor’s response due to its characteristic configuration.In addition,the one-step in situ microwave assisted process provides a promising and versatile choice for the preparation of gas sensing materials.
基金Supported by the National Natural Science Foundation of China(32072352)。
文摘In order to improve the quality of 3D printed raspberry preserves after post-processing,microwave ovens combining infrared and microwave methods were utilized.The effects of infrared heating temperature,infrared heating time,microwave power,microwave heating time on the center temperature,moisture content,the chroma(C*),the total color difference(ΔE*),shape fidelity,hardness,and the total anthocyanin content of 3D printed raspberry preserves were analyzed by response surface method(RSM).The results showed that under combining with the two methods,infrared heating improved the fidelity and quality degradation of printed products,while microwave heating enhanced the efficiency of infrared heating.Infrared-microwave combination cooking could maintain relatively stable color appearance and shape of 3D printed raspberry preserves.The AHP–CRITIC hybrid weighting method combined with the response surface test to determine the comprehensive weights of the evaluation indicators optimized the process parameters,and the optimal process parameters were obtained:infrared heating temperature of 190℃,infrared heating time of 10 min and 30 s,microwave power of 300 W,and microwave heating time of 2 min and 6 s.The 3D printed raspberry cooking methods obtained under the optimal conditions seldom had color variation,porous structure,uniform texture,and high shape fidelity,which retained the characteristics of personalized manufacturing by 3D printing.This study could provide a reference for the postprocessing and quality control of 3D cooking methods.
基金the National Natural Science Foundation of China(No.52272009)the Henan Provincial Science and Technology Research Project(No.242102230151)+1 种基金the Henan Provincial University Science and Technology Innovation Team(No.25IRTSTHN009)the Key Scientific Research Projects of Colleges and Universities in Henan Province(Nos.24B560021,25B560020,25B560023)。
文摘This paper adopted the hydrothermal method to prepare tungsten oxide(WO_(3))nanorod films and studied the effects of precursor solution concentration(0.02,0.03,0.06 mol/L peroxytungstic acid)and annealing temperature(200,300,400℃)on their electrochromic properties.The microstructure characterization of WO_(3) films were performed using scanning electron microscope(SEM),X-ray diffraction(XRD),and transmission electron microscope(TEM),and their electrochromic properties were tested by combining an electrochemical workstation with an ultraviolet-visible spectrophotometer.The results showed that the precursor solution concentration directly affected the thickness(290,560,990 nm)and microstructure of WO_(3) films,significantly impacting their electrochromic properties.However,the annealing temperature had a negligible effect.As the precursor solution concentration increased,the optical modulation of WO_(3) films gradually decreased,reaching 51.1%,43.8%,and 35.1%,respectively.The switching time first increased and then stabilized,with coloring times of 7.3,7.7,and 7.7 s,respectively,and bleaching times of 3.8,6.5,and 6.5 s,respectively.The coloration efficiency gradually increased but the increase was relatively small,reaching 41.8,44.4,and 44.8 cm^(2)/C,respectively.Moreover,the cycling stability of WO_(3) films was poor,with the ratios of the final value of optical modulation to the initial value 0.33,0.26,and 0.34,respectively.Additionally,there were bigger differences in the bleached state transmittance,while the colored state transmittance showed smaller variations.However,the former has better cycling stability than the latter.In summary,to obtain better electrochromic properties,the thickness of WO_(3) films should not exceed 290 nm.
文摘It was focused on the applications and developments of microwave hydrothermal synthesis piezoelectric ceramic powder. The microwave hydrothermal vessel was designed and manufactured. The microwave hydrothermal synthesis system was established and the PZT piezoelectric ceramic powder was synthesized. XRD and TEM have been used to characterize the products in detail. The diameter of the PZT powder particle is from 40 to 60 nm.
基金support of Project Supported by the Natural Science Foundation of China(Nos.51502163 and 51502165)Keypoint Research and Invention in Shaanxi Province of China(No.2017GY-186)the Scientific Research Foundation for the Returned Overseas Chinese Scholars,State Education Ministry
文摘In this study, SnNb_2O_6 and Sn_2Nb_2O_7 nanosheets are synthetized via microwave assisted hydrothermal method, and innovatively employed as anode materials for lithium-ion battery. The SnNb_2O_6 electrode exhibits high reversible capacity and excellent cycling stability(498 mAh/g at 0.1 A/g after 100 cycles),which is superior to that of Sn_2Nb_2O_7 electrode(173 mAh/g at 0.1 A/g after 100 cycles). Even increasing the current density to 2.0 A/g, the SnNb_2O_6 electrode still delivers a reversible capacity up to 306 mAh/g.The rate performance of the SnNb_2O_6 electrode is also better than that of Sn_2 Nb_2O_7 electrode at different current densities from 0.1 A/g to 2.0 A/g. The enhanced electrochemical performance of SnNb_2O_6 nanosheets can be attributed to the unique layered structure, which is conducive to the diffusion of the lithium ions and the migration of electrons during discharge/charge.
基金supported by the National Natural Science Foundation of China (Nos.21972124,21603041)funded by the Priority Academic Program Development of Jiangsu Higher Education Institutionsupport received at the Testing Center of Yangzhou University。
文摘A large surface area with high active site exposure is desired for the nano-scaled electrocatalysts fabrica-tion.Herein,taking NiMoO_(4)nanorods for example,we demonstrated the advantages of the microwave-assisted hydrothermal synthesis method compared to the traditional hydrothermal approaches.Both monoclinic structured NiMoO_(4)in the nanorods morphology are found for these samples but it is more time-saving and efficient in the Ni-Mo synergism for the catalyst obtained by microwave-assisted hydrothermal syntheses method.When evaluated for urea oxidation,the current density can reach 130.79 mA/cm^(2)at 1.54 V,about 2.4 times higher than that of the counterpart catalyst(54.08 mA/cm^(2)).Moreover,largely improved catalytic stability,catalytic kinetics and rapid charge transfer ability are found on the catalyst obtained by the microwave-assisted approach.The high catalytic performance can be at-tributed to the high surface area and active site exposure of NiMoO_(4)nanorods formed by microwave irradiation.Considering the less time,facile synthesis condition and efficient components synergism,the microwave-assisted hydrothermal synthesis method might work better for the nanostructure electrocata-lysts fabrication.
基金financially supported by the National Natural Science Foundation of China(No.21403298)。
文摘In this study,flower-like MoS2 constructed by nanosheets was synthesized by a simple hydrothermal method.The hydrothermal process was optimized and the effects of hydrothermal condition,including reaction temperature,reaction time and the ratio of Mo source to S source(Mo:S)in precursor,on microwave absorption performances and dielectric properties were investigated.Our results showed that when the reaction temperature was 180℃,the reaction time was 18 h,and the Mo:S was 1:3.5,the synthesized MoS2 had the best performance:Its minimum reflection loss could reach-55.78 dB,and the corresponding matching thickness was 2.30 mm with a wide effective bandwidth of 5.17 GHz.Further researches on the microwave absorption mechanism revealed that in addition to the destructive interference of electromagnetic waves,various polarization phenomena such as defect dipole polarization were the main reasons for microwave loss.We believe that MoS2 is a candidate for a practical microwave absorbent.
文摘Microwave-induced nitrogen-doped titanate nanotubes(NTNTs) were characterized by transmission electron microscopy(TEM), X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), Fourier transform infrared spectroscopy(FT-IR), Zeta potential analysis,specific surface area(SBET), and UV-Visible spectroscopy. TEM results indicate that NTNTs retain a tubular structure with a crystalline multiwall and have a length of several hundred nanometers after nitrogen doping. XRD findings demonstrate that the crystalline structure of NTNTs was dominated by anatase, which is favored for photocatalytic application. The Ti-O-N linkage observed in the XPS N 1s spectrum is mainly responsible for narrowing the band gap and eventually enhancing the visible light photoactivity. FT-IR results demonstrated the existence of H3O+, which could be excited by photo-generated holes to form hydroxyl radicals and degrade environmental pollutants. After sintering at 350°C, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which indicates N atom doping into the nanotubes. Photocatalytic degradation of Rhodamine B(RhB) via NTNTs show good efficiency, with pseudo first-order kinetic model rate constants of 3.7 × 10-3, 2.4 × 10-3and 8.0 × 10-4sec-1at pH 3, 7, and 11, respectively.
基金Project supported by the Natural Science Foundation of Heilongjiang Province(E201323)the Science and Technology Research Program of Education Bureau of Heilongjiang Province(12531213)
文摘Effects of La, N, and P doping on the structural, electronic and optical properties of TiO_2 synthesized from TiCl_4 hydrolysis via a microwave-hydrothermal process were investigated by X-ray diffraction, transmission electron microscopy, N_2 adsorption-desorption isotherm, X-ray photoelectron spectroscopy, electron paramagnetic resonance, UV-vis absorbance spectroscopy, photoelectrochemical measurements, and photoluminescence spectroscopy. The results showed that the presence of La in the tri-doped TiO_2 played a predominant role in inhibiting the recombination of the photogenerated electrons and holes. The existence of the substitutional N, interstitial N, and oxygen vacancies in TiO_2 lattices led to the band gap narrowing. It was P-doping rather than La or N doping that played a key role in inhibiting both anatase-to-rutile phase transformation and crystal growth, in stabilizing the mesoporous textural properties, and in increasing the content of surface bridging hydroxyl. Moreover, the tri-doping significantly enhanced the surface Ti^(4+)-O^(2-)-Ti^(4+)-O^(-·) species. All above-mentioned factors cooperated to result in the enhanced photoactivity of the tri-doped TiO_2. As a result, it exhibited the highest photoactivity towards the degradation of 4-chlorophenol(4-CP) under visible-light irradiation among all samples, which was much superior to commercial P25 TiO_2.
基金Supported by the National Natural Science Foundation of China(Nos.20775076 and 20875084)the National Technology Research & Development Program in the 11th Five-Year Plan of China(No.2006BAK10B09)
文摘We have developed a microwave-assisted hydrothermal method,where both microwave and hydrothermal techniques are utilized to synthesize CdTe nanocrystals with high quality in less than 55 s.Among the known preparation methods,the monodisperse CdTe nanocrystals showing narrow emission spectra,widest scope of emission peak(from 500 nm to 822 nm) and high quantum yield(up to 80%) were synthesized by this route.The quantum yield of CdTe with near-infrared emission(800 nm) is up to 10%,which is better than that of InAs(0.5%―2%) synthesized in organic phase.Moreover,we detected the latent fingerprints on aluminum,plastic,glass and papers by prepared CdTe nanocrystals,and photoluminescence fingerprints images were taken with a digital camera.Then the images would transmitt into fingerprint detection system of computer to identify the criminals in suit.
基金supported by the National Natural Science Foundation of China(21307012)Educational Commission of Fujian Province(JK2013007,2014J01035,JA15138)
文摘Bi(0.76)Sb(1.24)S3 nanocrystals were synthesized by a rapid microwave-assisted hydrothermal method using bismuth nitrate, antimony pentoxide and thioacetamide as starting materials and characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and UV-vis diffuse reflectance spectroscopy(DRS). The effects of the synthetic condition on the product composition were investigated. The photocatalytic activities of Bi(0.76)Sb(1.24)S3 nanocrystals for the degradation of methyl orange and p-hydroxyazobenzene under visible light irradiation were evaluated. Bi(0.76)Sb(1.24)S3 exhibited good and stable visible light photocatalytic activity.