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Co-existing air pollutants, especially NO x and VOCs, will generate secondary photochemical pollution under light irradiation. However, simultaneous elimination of multi-pollutants has long been a challenge. Photocatalysis could turn the reaction pathway between pollutants to convert them into harmless products, which is a promising technology for multi-pollutant control. Here we achieved synergistic photocatalytic degradation of NO and C 7 H 8 on InOOH photocatalyst, and the performance can be adjusted by H 2 O through affecting the interaction between surface species and catalyst. In situ DRIFTS and GC-MS revealed that the improved efficiency originated from the fast conversion of C–N coupling intermediates led by additional H 2 O. Surface characterizations and DFT simulation determined that accumulated nitrates will compete with the adsorption of NO and C 7 H 8 , resulting in a decline in efficiency in the later stage. Although improved efficiency would bring more nitrates, as H 2 O has comparable adsorption to nitrate at the same site, high humidity can mitigate the deactivation. The photocatalyst can be also simply regenerated by water washing. This work reveals the complex interaction in the multi-pollutant system and provides guidelines for precisely regulating the synergistic removal of NO x and VOCs. [Display omitted] • Synergistic removal of NO x and C 7 H 8 are achieved on InOOH. • H 2 O has a promotion effect on the simultaneous degradation of NO and C 7 H 8. • The enhanced removal originated from the fast conversion of C–N species. • The nitrate would compete with NO and C 7 H 8 adsorption and is the deactivation factor. • H 2 O has comparable adsorption to nitrate at the same site, thus can mitigate the decline in efficiency. [ABSTRACT FROM AUTHOR]

Surface hydroxyl groups play a decisive role in the generation of hydroxyl radicals with stronger oxidizing ability, which is indispensable in photocatalytic VOCs removal, especially under the condition of low humidity. In this work, non-noble amorphous SnO 2 decorated ZnSn(OH) 6 (ZSH) was synthesized by an in-situ method. The charge transport, reactant activation and hydroxyl polarization are enhanced through decoration of amorphous SnO 2 on ZSH. Combined with the designed experiment, in-situ EPR, DTF calculation and in-situ DRIFTS, the role and mechanism of interfacial hydroxyl polarization are revealed on SnO 2 decorated ZnSn(OH) 6. Compared with pristine ZSH and noble-metal modified ZSH, the toluene degradation rate of amorphous SnO 2 decorated ZSH is increased by 13.0 and 3.8 times, and the toluene mineralization rate is increased by 5.2 and 2.2 times. The ZSH-24 sample maintains a high toluene degradation activity after 6 cyclic utilization without catalyst deactivation. This work emphasizes the role of non-noble metal and the origin of hydroxyl group polarization on ZnSn(OH) 6 for photocatalytic VOCs mineralization. [Display omitted] • Amorphous SnO 2 decorated ZnSn(OH) 6 was synthesized by an in-situ method. • Photocatalytic mineralization of toluene is promoted via SnO 2 decoration. • Amorphous SnO 2 enhances charge transport and reactant activation on ZnSn(OH) 6. • The role and mechanism of hydroxyl polarization are clarified in detail. • The mechanism of photocatalytic toluene mineralization is revealed. [ABSTRACT FROM AUTHOR]

Aromatic hydrocarbon is a representative type of VOCs, which causes adverse effects to human health. The degradation stability of aromatic hydrocarbon is of vital importance to commercializing a photocatalyst for its practical application. The most commonly used titanium dioxide photocatalyst (P25) was deactivated rapidly in the photocatalytic VOCs degradation process. In this work, the indium hydroxide (In(OH) 3) photocatalyst was developed, which exhibited not only higher efficient activity but also ultra-stable stability for degradation of benzene, toluene and their mixtures. The origin of the activity difference between two catalysts was investigated by combined experimental and theoretical ways. Based on in situ DRIFTS and GC-MS, it was revealed that benzoic acid and carbonaceous byproducts were specifically formed and accumulated on P25, which were responsible for deactivation of photocatalyst. In contrast, as revealed by both DFT calculations and experimental results, the reaction pathway with byproducts blocking the active sites can be thermodynamically avoided on In(OH) 3. This rendered high durability to In(OH) 3 photocatalyst in degradations of aromatic pollutants. The elucidation of deactivation-resistant effect and reaction mechanism as an ideal photocatalyst for practical usage were provided. [Display omitted] • Durable photocatalytic decomposition of VOCs was achieved on In(OH) 3. • The benzoic acid and carbonaceous byproducts were accumulated on P25. • The reaction pathway with byproducts can be avoided on In(OH) 3. • The reaction mechanisms of photocatalytic decomposition of VOCs was proposed. • The elucidation of deactivation-resistant mechanism on In(OH) 3 were proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photocatalytic degradation of toluene was promoted by oxygen vacancy on InOOH. • OVs also facilitated methyl oxidation with the enhanced selectivity for ring opening. • In situ DRIFTS dynamically tracked the formation of primary reaction intermediates. • The reaction mechanism involved in photocatalysis of toluene is elucidated. The potential of oxygen vacancies (OVs) has been demonstrated in controlling photocatalytic activities by altering the electronic and/or band structures of photocatalysts. The effects of oxygen vacancies on photocatalytic reaction processes are yet unclear. In this work, indium oxyhydroxide (InOOH), well known as a wide band p-block metal compound with OVs, was synthesized through a one-pot solvothermal method to explore the roles of OVs in photocatalytic oxidation and ring opening of toluene. The defect level introduced by OVs enhanced light absorption and charge carrier separation, while promoting the activation of reactants to generate active oxygen species. As such, the modified InOOH was validated to enhance the photocatalytic performance by lowering the reaction energy barrier of the key intermediates during toluene oxidation (relative to the pristine InOOH). More strikingly, the energy barrier for the formation of benzoic acid was reduced with the increasing number of OVs on InOOH (accompanied by the increases in the ring opening reaction rates), in line with the results derived from the in situ DRIFTS investigation and theoretical calculation. Accordingly, it is possible to explain the mechanism regulating the photocatalytic oxidation of toluene on defective InOOH. This work could provide an electronic insight into oxygen vacancy engineering as a new strategy to enhance the photocatalytic selectivity and activity for VOC degradation. [ABSTRACT FROM AUTHOR]

[Display omitted] Improving the selectivity of photocatalysis and reducing the generation of toxic by-products are the two key challenges for the development of highly efficient and stable photocatalysts. In this work, it was revealed that Zn-Ti-layered double hydroxide (ZT-LDH) photocatalyst, which generated less intermediates, showed better toluene degradation efficiency (removal ratio, 75.2%) and stability, compared with P25 (removal ratio, 10.9%). During the photocatalytic toluene degradation, benzaldehyde and benzoic acid were the main intermediates existed in the gas phase and on the surface of the catalyst, respectively. By combining experiments with theoretical calculation, it was found that the hydrogen atoms on the hydroxyl groups in the LDH would selectively attract the oxygen atoms in the carbon–oxygen double bond of the two major intermediates, facilitating their adsorption and activation on ZT-LDH. Besides, the surface electronic structure of ZT-LDH was demonstrated to facilitate the ring-opening reaction of the two major intermediates, eventually maintaining high activity and stability. This work could provide new molecular perspectives for understanding the photocatalytic reactions in VOCs degradation and developing efficient and stable photocatalysts. [ABSTRACT FROM AUTHOR]