Minimizing electron-hole recombination in modified TiO₂photocatalysis: electron transfer to solution as rate-limiting step in organic compounds degradation

Abstract

4‐Stilbenecarboxaldehyde (4SCA) at pH 3 was added to TiO2 anatase to form a new catalyst where the aldehyde carbonyl group reacts with the TiO2‐OH to form the corresponding acetal (4SCA‐TiO2). 4SCA‐TiO2 significantly retards the electron recombination when it is illuminated with ultraviolet B light because of the formation of a stable radical anion·−4SCA‐TiO2 that we have detected spectroelectrochemically. The light excited electron on the catalysis is transferred relatively slow to solution. Therefore, the electron transfer to solution is the rate‐limiting step for water‐dissolved organic compound degradation when 4SCA‐TiO2 is used as photocatalyst. For instance, degradation rate constants using naphthalene (Naph) and p‐nitrophenol (PNP) in an ample pH range support the proposal. Accordingly, rate constants are faster when the standard redox potential of the involved electron acceptor in the solution increases. In fact, this condition can be tuned to promote reactivity. The affinity between the organics being degraded and 4SCA‐TiO2 also influences on the degradation rate constants.

Unprecedented large solvent (H2O vs D2O) isotope effect in semiconductors photooxidation

“…Alternatively, acid conditions might favor others electrolytes reduction and/or stabilize Bi 2 WO 6 valence band energy what favor oxidation at the photogenerated hole . However, at the conditions in which the isotope solvent effect was measured, pH = 7, these possibilities are reduced.…”

“…O 2 reduction rates have been determined at several electrode potentials and oxygen concentrations. Additionally, we have used open circuit potential decay technique to determine the rate of electron decay once the circuit is open and illumination is turned off . These potential decay measurements may also account for the observed rates of electron transfer to solution under conditions in which the e − /h + recombination is minimized.…”

“…These potential decay measurements may also account for the observed rates of electron transfer to solution under conditions in which the e − /h + recombination is minimized. In these conditions, a dependence of the photocatalytic process with the modified catalyst surface and the electron acceptor in solution yields a linear energy correlation.…”

Piezoelectrically Enhanced Photocatalysis with BiFeO3 Nanostructures for Efficient Water Remediation

“…To overcome this problem, wide bandgap semiconductors, such as titanium dioxide (TiO 2 ), are extensively used. However, having a wide bandgap limits the light absorption of these materials to the UV region ( Núñez et al., 2017 ). Hence, researchers have proposed new strategies, including developing novel nanostructures, using co-catalysts (Pt, Pd, and RuO 2 ), doping with rare-earth or transition metals, and fabricating heterojunctions to tune the bandgap of these materials, to lower the electron-hole recombination rate, and to increase the lifetime of the charge carriers ( Long and Prezhdo, 2015 , Sakthivel et al., 2004 , Mushtaq et al., 2015 , Mushtaq et al., 2016 , Zhang et al., 2011 ).…”

Enhanced Enzymatic Hydrolysis of Rice Straw Pretreated by Oxidants Assisted with Photocatalysis Technology

“…It is capable of indirect photolysis or heterogeneous photocatalysis when TiO 2 combines with ultraviolet (UV) light [ 12 ]. It is generally accepted that OH radical oxidation and electron–hole reaction occur due to the short wavelength of UV light to complete the photolysis process [ 13 ], and show very fast reaction rates [ 14 , 15 ]. Several groups have used the pretreatment technology of TiO 2 /UV to degrade organic contaminants [ 16 , 17 ], and the TiO 2 /UV process can successfully pretreat paper mill effluent, black liquor, and olive mill waste water [ 10 , 18 ].…”