Diverting the use of reduced TiO2 from a carrier of electron-hole pairs to a reservoir of Bronsted-Lewis acidic pairs for sustainable, non-optical H2O2 homolysis

초록

Defective TiO2 bears intra-bandgap states (INTRA) and a valence band (VB) that host electrons and holes, respectively, upon photo-excitation, enabling (OH)-O-center dot/O-2(center dot-)/O-1(2) formation via semi-conducting pathways. However, the energetic window of INTRA/VB is often narrow or mismatches with that of semi-conducting pathways, restricting (OH)-O-center dot/O-2(center dot-)/O-1(2) generation. Here, TiO2 was calcined at 300 degrees C (O300) and reduced at 300-600 degrees C (R300-R600) to tune quantities (N)/strengths (E) of Brosted acidic (BA(-)-H+) and Lewis acidic sites with coordination numbers of 5 (LA(I)) or <= 4 (LA(II)). The catalysts revealed distinct N/E values with hierarchies of N-LAII < N-LAI << N-BA--H(+) or E-BA--H(+) < E-LAI similar to E-LAII. Non-photonic H2O2 homolysis (H2O2 -> 2(center dot)OH) proceeded via BA(-)-H+/LA(II), yet hinged on BA(-)-H+ with E-BA--H(+) and N-BA--H(+) dictating the energy barrier (E-BARRIER) and lumped collision frequency , respectively, as corroborated by the H2O2 consumption rate (-r(H2)O(2)) law. -r(H2)O(2) values of O300/R300/R600 were challenging to assess, thus being assessed using their initial acetaminophen degradation rates in a per-BA(-)-H+ site (-r(ACETAMINOPHEN, 0, CO2)) or on a per-gram basis (-r(ACETAMINOPHEN, 0)). R600 showed the highest E-BA--H(+) and smallest N-BA--H(+), thus yielding the lowest E-BARRIER and lowest , respectively, where the former overrode the latter to achieve the highest -r(ACETAMINOPHEN, 0, CO2) for R600. R600 displayed the highest resistance to the deposition of poisonous oligomer/(OOH)-O-center dot on BA(-)-H+/LA(II) or poisonous O-2 on LA(I) due to its smallest N-BA--H(+)/highest E-BA--H(+)/highest E-LAII for oligomer/(OOH)-O-center dot and the smallest N-LAI/highest E-LAI for O-2, as also substantiated by density functional theory calculations. Consequently, -r(ACETAMINOPHEN, 0) values of R600 were higher than those of O300/R300 throughout acetaminophen decomposition recycle runs, whereas R600 was moderately recovered upon regeneration. -r(POLLUTANT, 0, CO2) values of R600 were 2-23-fold and 3-10-fold higher than those of O300/R300 and ZrO2/UiO-66, respectively, in disintegration of diverse aqueous pollutants (analgesic/endocrine disruptor/pesticide/antibiotic).

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