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The universal limit on the pH conditions is disturbing peroxymonosulfate (PMS)-triggered high-valent iron-oxo systems in environmental applications. Here, we propose for the first time the construction of a neutral microenvironment on the surface of Zn-Fe layered double hydroxide (ZnFe-LDH) by using the amphoteric properties of zinc hydroxide, which continuously generates ≡Fe IV =O over a wide pH range of 3.0-11.0 in activating PMS. The ≡Zn(OH) 2 moiety offers a neutral microenvironment at the phase interface, which mitigates the self-decomposition of ≡Fe IV =O by protons and the hydrolysis reaction of iron by hydroxyl groups, which is supported by the Mossbauer spectra, density functional theory calculations and designed experiments. Consequently, ZnFe-LDH/PMS can satisfy the stability in long-term experiments, selectivity under conditions with high salinity or natural organic matter and efficient treatment of actual wastewater., (© 2022 Wiley-VCH GmbH.)

It is important to develop self-producing reactive oxygen species (ROSs) systems and maintain the continuous and effective degradation of organic pollutants. Herein, for the first time, a system of ultrasound-treated CoS 2-x mixed with Fe 2+ is constructed to sustainably release singlet oxygen ( 1 O 2 ) for the effective degradation of various organic pollutants, including dyes, phenols, and antibiotics. Ultrasonic treatment produces defects on the surface of CoS 2 which promote the production of ROSs and the circulation of Fe 3+ /Fe 2+ . With the help of Co 4+ /Co 3+ exposed on the surface of CoS 2-x , the directional conversion of superoxide radical ( . O 2 - ) to 1 O 2 is realized. The CoS 2-x /Fe 2+ system can degrade organic pollutants efficiently for up to 30 days, which is significantly better than the currently recognized CuP x system (<3 days). Therefore, CoS 2-x provides a new choice for the long-term remediation of organic pollutants in controlling large area river pollution., (© 2020 Wiley-VCH GmbH.)

The abuse of fossil fuels release large amount of CO 2 , causing intense global warming. Using photoreduction and electroreduction to convert CO 2 into highly valuable fuels such as CO and CH 4 can effectively solve this problem. However, due to the limited activity and selectivity, pristine catalyst materials cannot meet the requirements of practical applications, which means that some modifications to these catalysts are necessary. In this review, a series of research reports on oxygen defect engineering have been introduced. First, the methods of preparing oxygen defects by heat treatment, doping, and photoinduction combined with influencing factors in the preparation are introduced. Subsequently, common characterization methods of oxygen defects including EPR, Raman, XPS, EXAFS, and HRTEM are summarized. Finally, the mechanisms of introducing oxygen defects to improve CO 2 reduction are discussed, and include enhancing light absorption, improving CO 2 adsorption and activation, as well as promoting stability of the reaction intermediates. The summary of research on oxygen defects provides guidance for researchers who focus on CO 2 reduction and accelerate the realization of its industrial applications in the future., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

3D-MoS 2 can adsorb organic molecules and provide multidimensional electron transport pathways, implying a potential application for environment remediation. Here, we study the degradation of aromatic organics in advanced oxidation processes (AOPs) by a 3D-MoS 2 sponge loaded with MoS 2 nanospheres and graphene oxide (GO). Exposed Mo 4+ active sites on 3D-MoS 2 can significantly improve the concentration and stability of Fe 2+ in AOPs and keep the Fe 3+ /Fe 2+ in a stable dynamic cycle, thus effectively promoting the activation of H 2 O 2 /peroxymonosulfate (PMS). The degradation rate of organic pollutants in the 3D-MoS 2 system is about 50 times higher than without cocatalyst. After a 140 L pilot-scale experiment, it still maintains high efficiency and stable AOPs activity. After 16 days of continuous reaction, the 3D-MoS 2 achieves a degradation rate of 120 mg L -1 antibiotic wastewater up to 97.87 %. The operating cost of treating a ton of wastewater is only US$ 0.33, suggesting huge industrial applications., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Advanced oxidation processes (AOPs) based on sulfate radicals (SO 4 ⋅- ) suffer from low conversion rate of Fe(III) to Fe(II) and produce a large amount of iron sludge as waste. Herein, we show that by using MoO 2 as a cocatalyst, the rate of Fe(III)/Fe(II) cycling in PMS system accelerated significantly, with a reaction rate constant 50 times that of PMS/Fe(II) system. Our results showed outstanding removal efficiency (96%) of L-RhB in 10 min with extremely low concentration of Fe(II) (0.036 mM), outperforming most reported SO 4 ⋅- -based AOPs systems. Surface chemical analysis combined with density functional theory (DFT) calculation demonstrated that both Fe(III)/Fe(II) cycling and PMS activation occurred on the (110) crystal plane of MoO 2 , whereas the exposed active sites of Mo(IV) on MoO 2 surface were responsible for accelerating PMS activation. Considering its performance, and non-toxicity, using MoO 2 as a cocatalyst is a promising technique for large-scale practical environmental remediation., Competing Interests: Declaration of Interests The authors declare no competing financial interest., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

The greatest problem in the Fe(II)/H 2 O 2 Fenton reaction is the low production of ·OH owing to the inefficient Fe(III)/Fe(II) cycle and the low decomposition efficiency of H 2 O 2 (<30%). Herein, we report a new discovery regarding the significant co-catalytic effect of WS 2 on the decomposition of H 2 O 2 in a photoassisted Fe(II)/H 2 O 2 Fenton system. With the help of WS 2 co-catalytic effect, the H 2 O 2 decomposition efficiency can be increased from 22.9% to 60.1%, such that minimal concentrations of H 2 O 2 (0.4 mmol/L) and Fe 2+ (0.14 mmol/L) are necessary for the standard Fenton reaction. Interestingly, the co-catalytic Fenton strategy can be applied to the simultaneous oxidation of phenol (10 mg/L) and reduction of Cr(VI) (40 mg/L), and the corresponding degradation and reduction rates can reach up to 80.9% and 90.9%, respectively, which are much higher than the conventional Fenton reaction (52.0% and 31.0%). We found that the expose reductive W 4+ active sites on the surface of WS 2 can greatly accelerate the rate-limiting step of Fe 3+ /Fe 2+ conversion, which plays the key role in the decomposition of H 2 O 2 and the reduction of Cr(VI). Our discovery represents a breakthrough in the field of inorganic catalyzing AOPs and greatly advances the practical utility of this method for environmental applications.

Photocatalytic reduction of CO 2 holds great promises for addressing both the environmental and energy issues that are facing the modern society. The major challenge of CO 2 photoreduction into fuels such as methane or methanol is the low yield and poor selectivity. Here, we report an effective strategy to enhance the reduction potential of photoexcited electrons by fluorination of mesoporous single crystals of reduced TiO 2- x . Density functional theory calculations and photoelectricity tests indicate that the Ti 3+ impurity level is upswept by fluorination, owing to the built-in electric field constructed by the substitutional F that replaces surface oxygen vacancies, which leads to the enhanced reduction potential of photoexcited electrons. As a result, the fluorination of the reduced TiO 2- x dramatically increases the CH 4 production yield by 13 times from 0.125 to 1.63 μmol/g·h under solar light illumination with the CH 4 selectivity being improved from 25.7% to 85.8%. Our finding provides a metal-free strategy for the selective CH 4 generation from CO 2 photoreduction.

A spatially separated, dual co-catalyst photocatalytic system was constructed by the stepwise introduction of RuO 2 and Au nanoparticles (NPs) at the internal and external surfaces of a three dimensional, hierarchically ordered TiO 2 -SiO 2 (HTSO) framework (the final photocatalyst was denoted as Au/HRTSO). Characterization by HR-TEM, EDS-mapping, XRD and XPS confirmed the existence and spatially separated locations of Au and RuO 2 . In CO 2 photocatalytic reduction (CO 2 PR), Au/HRTSO (0.8%) shows the optimal performance in both the activity and selectivity towards CH 4 ; the CH 4 yield is almost twice that of the singular Au/HTSO or HRTSO (0.8%, weight percentage of RuO 2 ) counterparts. Generally, Au NPs at the external surface act as electron trapping agents and RuO 2 NPs at the inner surface act as hole collectors. This advanced spatial configuration could promote charge separation and transfer efficiency, leading to enhanced CO 2 PR performance in both the yield and selectivity toward CH 4 under simulated solar light irradiation.

The preparation of reduced TiO 2 photocatalysts with high Ti 3+ concentration is a great challenge due to their instability in air. Here we report a new approach for the synthesis of reduced TiO 2 with {001} facets exposed via a hydrothermal process. By the introduction of fluoride atoms, {001} and {101} facets are formed, which act as hole and electron collectors, respectively, for charge separation. By adjusting the volume of HF added, a rutile-anatase transition is observed for the first time. EPR spectra confirm the generation of Ti 3+ species in the bulk of TiO 2 , and Ti 3+ signals are studied in the anatase and rutile phases separately. The quantified EPR shows that reduced TiO 2 samples present 14 000-fold more spins compared to the pristine TiO 2 , and the intensity can reach as high as 24.6 × 10 19 spins per g. The obtained samples also have a unique disordered layer with a thickness of 1-2 nm on their surfaces, which contributes to the stabilization of the formed Ti 3+ species by preventing their oxidation in air. In addition, the synthesized reduced TiO 2 samples also exhibit wide-spectrum solar light absorption, especially in the near-infrared region. Owing to their enhanced solar light absorption, improved electron-hole separation and special facet exposure, these samples exhibit enhanced photocatalytic CO 2 reduction performance and high CH 4 selectivity under solar light irradiation, in the absence of a noble metal Pt as a co-catalyst.

Hollow structures with an efficient light harvesting and tunable interior component offer great advantages for constructing a Z-scheme system. Controlled design of hollow cobalt sulfide (Co 9 S 8 ) cubes embedded with cadmium sulfide quantum dots (QDs) is described, using hollow Co(OH) 2 as the template and a one-pot hydrothermal strategy. The hollow CdS/Co 9 S 8 cubes utilize multiple reflections of light in the cubic structure to achieve enhanced photocatalytic activity. Importantly, the photoexcited charge carriers can be effectively separated by the construction of a redox-mediator-free Z-scheme system. The hydrogen evolution rate over hollow CdS/Co 9 S 8 is 134 and 9.1 times higher than that of pure hollow Co 9 S 8 and CdS QDs under simulated solar light irradiation, respectively. Moreover, this is the first report describing construction of a hollow Co 9 S 8 based Z-scheme system for photocatalytic water splitting, which gives full play to the advantages of light-harvesting and charges separation., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Cd x Zn 1-x Se/CoP composites have been well studied as effervescent photocatalysts for H 2 evolution. These composites are highly efficient at 45.1 mmol h -1 g -1 and have a high quantum yield of 11.8% at ∼520 nm. The tunable energy band of Cd x Zn 1-x Se facilitates photo-electrons transferring to CoP via chemical bonds between components. Advances in Cd x Zn 1-x Se/CoP for photocatalytic H 2 evolution provide a new strategy for future splitting of seawater.

A brown mesoporous TiO2-x /MCF composite with a high fluorine dopant concentration (8.01 at%) is synthesized by a vacuum activation method. It exhibits an excellent solar absorption and a record-breaking quantum yield (Φ = 46%) and a high photon-hydrogen energy conversion efficiency (η = 34%,) for solar photocatalytic H2 production, which are all higher than that of the black hydrogen-doped TiO2 (Φ = 35%, η = 24%). The MCFs serve to improve the adsorption of F atoms onto the TiO2 /MCF composite surface, which after the formation of oxygen vacancies by vacuum activation, facilitate the abundant substitution of these vacancies with F atoms. The decrease of recombination sites induced by high-concentration F doping and the synergistic effect between lattice Ti(3+)-F and surface Ti(3+)-F are responsible for the enhanced lifetime of electrons, the observed excellent absorption of solar light, and the photocatalytic production of H2 for these catalysts. The as-prepared F-doped composite is an ideal solar light-driven photocatalyst with great potential for applications ranging from the remediation of environmental pollution to the harnessing of solar energy for H2 production., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)