Metal−organic frameworks(MOFs),such as HKUST-1,have been used in many applications such as catalysis,gas capture,and more.However,one major limitation hindering their application is inherent chemical instability,and c...Metal−organic frameworks(MOFs),such as HKUST-1,have been used in many applications such as catalysis,gas capture,and more.However,one major limitation hindering their application is inherent chemical instability,and conducting in situ studies on their degradation with sufficient spatial-temporal resolution remains a challenge.In this work,we employ optical microscopy to quantitatively monitor the degradation of HKUST-1 under alkaline and acidic reducing environments with video-rate temporal resolution.By color-mapping the degradation progress over different time intervals with alkaline hole(h^(+))scavengers(sodium ascorbate,NaAs),we observe a sigmoidal time-dependent degradation trend.The results reveal the presence of confined regions with faster degradation.It is discovered that degradation begins with the chemical reduction of HKUST-1 into Cu_(2)O nanoparticles,followed by self-photoreduction into Cu_(2)O/Cu.Furthermore,it is observed that there is a h+scavenger concentration and laser-wavelength-dependent degradation.At higher concentrations and irradiation energy,there is faster degradation in the HKUST-1 framework.Under acidic reducing conditions with lactic acid(LA),the degradation rate constant is 22% higher than that under alkaline conditions,while the valence state of Cu remains unchanged.This can be attributed to distinct degradation mechanisms at different pH levels,in which acidolysis and metal−ligand disruption dominate in the presence of LA,while HKUST-1 degradation is primarily redox-driven in NaAs solution.These findings offer mechanistic insight into the degradation behavior of HKUST-1 and provide valuable guidance for optimizing MOF stability in practical applications.展开更多
基金support from the Ministry of Education,Singapore,under its Academic Research Fund Tier 1(No.RG60/21,RG1/23,RG9/24)the Singapore Agency for Science,Technology and Research(A*STAR)MTC IRG grant(No.M21K2c0110).
文摘Metal−organic frameworks(MOFs),such as HKUST-1,have been used in many applications such as catalysis,gas capture,and more.However,one major limitation hindering their application is inherent chemical instability,and conducting in situ studies on their degradation with sufficient spatial-temporal resolution remains a challenge.In this work,we employ optical microscopy to quantitatively monitor the degradation of HKUST-1 under alkaline and acidic reducing environments with video-rate temporal resolution.By color-mapping the degradation progress over different time intervals with alkaline hole(h^(+))scavengers(sodium ascorbate,NaAs),we observe a sigmoidal time-dependent degradation trend.The results reveal the presence of confined regions with faster degradation.It is discovered that degradation begins with the chemical reduction of HKUST-1 into Cu_(2)O nanoparticles,followed by self-photoreduction into Cu_(2)O/Cu.Furthermore,it is observed that there is a h+scavenger concentration and laser-wavelength-dependent degradation.At higher concentrations and irradiation energy,there is faster degradation in the HKUST-1 framework.Under acidic reducing conditions with lactic acid(LA),the degradation rate constant is 22% higher than that under alkaline conditions,while the valence state of Cu remains unchanged.This can be attributed to distinct degradation mechanisms at different pH levels,in which acidolysis and metal−ligand disruption dominate in the presence of LA,while HKUST-1 degradation is primarily redox-driven in NaAs solution.These findings offer mechanistic insight into the degradation behavior of HKUST-1 and provide valuable guidance for optimizing MOF stability in practical applications.
