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Chromite ore processing residue (COPR) is an environmental threat due to its content of Cr (Ⅵ) which is a highly toxic substance. However, some metallic elements in COPR can create the intrinsic values of COPR. In this study, the nano-lead chromate (PbCrO 4) was prepared by the chemical precipitation method for the water-soluble Cr (VI) leachate obtained by the simple water washing of COPR and the use of methylene blue (MB) degradation. Results demonstrated that the prepared lead chromate had good photocatalytic performance and stability. The degradation rate of MB was 76.78% with the conditions of the initial pH was 6, the initial concentration was 10 mg/L, the reaction time was 80 min, and the photocatalyst dosage was 1.0 g/L. Moreover, recycling results displayed that the degradation rate remained at 62.91% after five cycles which means it can be recycled. Meanwhile, the concentration of Cr (VI) in COPR decreased from 34.7 to 1.4 mg/L which is below the national emission standard of China (GB 5085.3–2007), that is 5 mg/L, achieving harmless treatment of COPR. Consequently, this study provides a new tactic for the resource utilization of COPR, and implements the governance concept of "waste control by turning waste into treasure". [Display omitted] • The water-soluble Cr (VI) was leachate obtained by simple water washing of COPR. • Nano-PbCrO 4 was successfully prepared using water-soluble Cr (VI) as raw material. • The nano-PbCrO 4 was applied to methylene blue (MB) degradation. • The main influencing factors, mechanism, and stability were studied. [ABSTRACT FROM AUTHOR]

Fe, Co, N atoms co-doped hollow carbon capsules was prepared and used as metal-free catalysts for PMS activation. In Fenton-like reaction, it displayed high degradation rate and outstanding adaptation to full pH range (0–14). [Display omitted] • Fe-Co-N@HCCs displays high PMS activation property in a full range of pH values. • k of Fe-Co-N@HCC is 3.1 and 1.4 times higher than N@HCCs and Fe-N@HCCs. • Contribution of radicals, 1O 2 , electron-transfer path is 13.3%, 30.1%, 56.6%. • PMS is activated on Fe-N 4 and Co-N 4 sites for 1O 2 , Co-N 4 site shows better activity. • Leached Fe and Co ions is 24.9 and 13.6 times lower than Fe-Co-N@HCCs/FeCo. Persulfate (PMS)-based Fenton-like reaction was a highly efficient technique for disposal of organic contaminants. However, high metal leaching and low environmental adaptation were the major concerns for further application. To overcome these two drawbacks, herein, Fe, Co, N atoms co-doped hollow carbon capsules (Fe-Co-N@HCCs) were prepared and used as catalysts for PMS activation. 92.6% of TC was degraded within 40 min and the mineralization efficiency was 55.7%. The degradation rate was 4.7, 3.1 and 1.4 times higher than those of activated carbon, N@HCCs, and Fe-N@HCCs, respectively. Thermodynamic study indicated the TC degradation was an exothermal, chaotic and non-spontaneous process. Radical trapping experiments, electron paramagnetic resonance spectrum, and electrochemical analysis indicated that 1O 2 production and electron-transfer path worked together for PMS activation. DFT calculation indicated that the catalytic activity of Co-N 4 site was higher than Fe-N 4 site for 1O 2 production. Fe-Co-N@HCCs were adapted well to the full pH range (0–14) and complex inorganic anions via non-radical PMS activation paths. Meanwhile, the leached Fe and Co ions were lowered to 0.201 and 0.457 mg/L, satisfying the China emission standard. This work gave a better comprehension on preparation of carbonaceous materials with high environmental adaptation and low leached metal ions for PMS activation. [ABSTRACT FROM AUTHOR]

Using solar energy to catalyse photo-driven processes to address the energy crisis and environmental pollution plays a role in the path to a sustainable society. Many oxide-based materials, especially perovskite oxides, have been widely investigated as catalysts for photocatalysis in energy and environment because of the low-cost and earth-abundant and good performance. At this stage, there is a need to present a scientific-based evaluation of the technologies developed so far and identify the most sustainable technologies and the existing limitations and opportunities for their commercialisation. This work comprehensively investigated the outcomes using various scientometric indices on perovskite oxide-based photo(electro)catalysts for water splitting, nitrogen fixation, carbon dioxide conversion, organic pollutant degradation, current trends and advances in the field. According to the results achieved, efforts in both energy and environment based on perovskite oxides have been initiated in the 1990s and accelerated since the 2010s. China and the United States were identified as the most contributing countries. Based on the results achieved in this study, the main milestones and current trends in the development of this field have been identified. The aim of this research is to provide useful guidelines for the further investigation of perovskite oxide-based catalysts for photoelectrocatalysis and photocatalysis both in energy and environment on the applications such as water splitting, nitrogen fixation, carbon dioxide conversion, and wastewater treatment. [ABSTRACT FROM AUTHOR]