Solar-assisted photocatalytic water splitting using defective UiO-66 solids from modulated synthesis

Metal-organic frameworks(MOFs)are attracting increasing interests as photocatalysts for solar-driven hydrogen production from water.This paper reports on a comparative study of using either acetic acid(AA)or trifluoroacetic acid(TFA)as the representative UiO-66 organic modulators for synthesizing visible light responsive UiO-66(Zr)-X(X:NH_(2) or NO_(2))photocatalysts for water splitting.The results show that photocatalytic hydrogen generation from a water/methanol mixture can be improved by varying the nature and amount of the modulator employed to prepare the different UiO-66(Zr)-X(X:NH_(2) or NO_(2))solid derivatives.UiO-66(Zr)-NH_(2) was the most active photocatalyst,followed by UiO-66(Zr)-NO_(2),both prepared with 12 equivalents of AA with respect to the organic ligand.This UiO-66(Zr)-NH_(2) solid was more active than the parent MOF in photocatalytic overall water splitting(OWS)(H_(2) and O_(2) production of 450 and 160μmol·g^(-1),respectively,in 5 h;apparent quantum yield(AQY)at 400 nm of 0.06%)in the absence of methanol and compares favourably with analogous reports.Information on the photocatalytic activity of the most active solids of both series was obtained by means of a series of techniques,including ultraviolet-visible(UV-vis)diffuse reflectance,X-ray photoelectron spectroscopy(XPS),laser flash photolysis(LFP),electron spin resonance(ESR),photoluminescence and photoelectrochemical measurements together with density functional theory(DFT)calculations.The results showed that organic acid modulators can be used to enhance the photocatalytic activity of missing linker UiO-66 defective materials in solar-powered water splitting.

Robust hybrid bismuth perovskites as potential photocatalysts for overall water splitting

Organic-inorganic hybrid perovskites have gained great attention as promising photocatalysts for hydrogen generation.However,due to their poor stability in water,the use of aqueous hydrohalic acid solutions is specifically required for an efficient hydrogen evolution.Herein,three novel photoactive lead-free hybrid perovskites based on bismuth and triazolium cations(denoted as IEF-15,IEF-16,and IEF-17(IEF stands for IMDEA energy frameworks))were synthesized and fully characterized(structural,compositional,optical,etc.).Further,these solids were proposed as photocatalysts for the challenging gas phase overall water splitting(OWS)reaction.Accordingly,IEF-16 thin films exhibited a remarkable photocatalytic activity in both H_(2) and O_(2) evolution,as a consequence of its appropriate bandgap and energy-band alignment,achieving hydrogen evolution rates ofμmol·g_(H_(2))^(-)1846 and 360 after 24 h under ultraviolet-visible(UV-vis)irradiation or simulated solar irradiation,respectively.This study additionally highlights the remarkable structural and photochemical stability of IEF-16 under different operational conditions(i.e.water volume,irradiation and temperature),paving the way for green hydrogen production from OWS using perovskite-based photocatalysts.