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• The catalyst activated PDS efficiently with high stability and generalizability. • The complexation of AL with RM favored the exposure of Fe active sites and adsorption of PDS. • The electron transfer pathway was the main pathway for PDS activation and SMZ degradation. • DFT demonstrated that Fe-active species are the primary site where electron transfer occurs. • T.E.S.T and biological experiments predicted lower toxicity of degradation intermediates. Advanced oxidation processes based on peroxydisulfate (PDS-AOPs) have been used for the remediation of organic wastewater. However, the mechanism for the generation of electron transfer sub-stable complexes in the metal–carbon/PDS system has not been fully elucidated. Herein, two environmental solid wastes were selected to synthesize a novel Fe-carbon catalyst (RM@KC 1:2 –800) using alkali lignin as the carrier and red mud (RM) as the iron source, and applied for peroxydisulfate (PDS) activation in sulfamethazine (SMZ) removal. The complexation of alkali lignin with RM favored the exposure of Fe active sites and adsorption of PDS. 97% of SMZ could be removed efficiently in the RM@KC 1:2 –800/PDS system, and the degradation efficiency remained at 80.81% after 5 cycles without metal leaching, which was suitable for a variety of natural water bodies. Combined with density functional theory (DFT) and other analyses confirmed that the electron transfer pathway is the main pathway for PDS activation and SMZ degradation. And the reactive Fe species were the active sites that contributed to the adsorption of PDS on the RM@KC 1:2 –800 surface to form sub-stable complexes (RM@KC-PDS*), whereby the electron transfer occurred. Surprisingly, the prediction of environmental toxicity of the degradation intermediates based on T.E.S.T software and biological experiments proved their environmental friendliness. Overall, this study follows the concept of "waste-to-waste" and proposes a strategy for a suitable and cost-effective Fe-carbon catalyst for large-scale production, while demonstrating its potential application in the treatment of organic wastewater. [ABSTRACT FROM AUTHOR]

• Modes of natural and industrial degradation of lignin are reviewed. • The changes of lignin structure and properties by organic solvent extraction and ionic liquid isolation are reviewed. • Organic solvent extraction can retain the inherent structure of lignin to the greatest extent and exploit native activity. • The types of products vary with the types of ionic liquids. • The challenges of lignin separation methods and the future development of ionic liquids are reviewed. The complex interlacing structure among cellulose, hemicellulose and lignin and the unique properties of lignin itself limit the value-added utilization of the lignin. As the "upstream" process of biorefinery, lignin separation technology is very important for lignin conversion into high-value materials. However, it is not easy to extract lignin with relatively complete structure without affecting performance from biomass raw materials. Notably, most of reviews regarding lignin focus on its degradation. The extraction or separation methods are not introduced in detail, and the effects of these methods on raw materials or lignin have not been reported. Herein, this paper critically reviews the changes in physicochemical properties and structure of lignin caused by several mild organic solvent extraction methods and new ionic liquids which has been widely used in recent years. Furthermore, the application and potential economic benefits of these lignin are summarized. These methods promote the effective utilization of lignin, which is no longer limited to heat energy, but also alleviates the solid waste disposal problem caused by lignin as waste stream. Finally, perspectives on the future research on the lignin separation, depolymerization and application are highlighted. This review may provide an insight for the development of bio-refining technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lamellar cluster LDH in situ grew on the MIL-88A template. • Dispersed LDH covers stably activate PMS at wide circumneutral pH from 2.5 to 10.5. • Disequilibrium of hydrolysis-precipitation in limit pH caused catalysis declines. • ROSs reconfiguration and dissociable SMT reactivity were examined in limited pH. • Toxicity of structural rearrangements in sulfonamide moiety was revealed. The development of effective and reliable Fenton-like catalytic systems in circumneutral pH is a longstanding interest. Metal-organic framework derivatives become promising catalyst candidates due to high catalytic accessibility and structural flexibility, but their stability remains in doubt. Herein, a MIL-88A self-templating strategy to synthesize structurally decentralized FeCo-layered-double hydroxide (FeCo-LDH, M−FCL) was proposed. The well-constructed M−FCL 3 presented superior peroxymonosulfate (PMS) activation for nearly 100 % sulfamethazine (SMT) degradation within 15 min, which was virtually wobble-slight in the pH = 2.5 ∼ 10.5 range. The performance decrease at limiting pH was mainly ascribed to activity-blocked of M−FCL 3 by analyzing the involved reaction substrates and reactive oxygen species. In specific, the hydrolytic detachment or excessive aggregation of surface-active FeCo-LDH occurred at limiting pH with unbalanced hydrolysis-coprecipitation. Especially, theoretical calculations further exposed that the loss of dominated active Co site and the formation of inert SMT+ dissociating species were detrimental to the catalytic process in acidic environments. Nevertheless, the well-founded resistance of the constructed M−FCL 3 /PMS system to interference and its ability to operate for a long period proved its potential for application in near-neutral environments. This work raised concern for the variations of Fenton-like catalysis at limiting pH, promoting the application of MOF-derived LDH for environmental remediation. [ABSTRACT FROM AUTHOR]

[Display omitted] • The promoted generation strategies of 1O 2 in PS activation by modified-nZVI systems and nZVI-based coupling systems are summarized. • The influence factors on the generation and behavior of 1O 2 in nZVI/PS-based systems are reviewed. • The selectivity, wide pH adaptability and corresponding roles of 1O 2 in organic pollutants degradation are reviewed. • The challenges and prospects of 1O 2 generation in nZVI/PS-based systems are addressed. In recent years, the remediation of water contamination through non-radical pathways by singlet oxygen (1O 2) has caught scientists' increasing attention owing to the adaptability to wider pH range and superior selectivity to target pollutants. In this review, strategies of promoting the generation of 1O 2 in persulfate activation over nanoscale zero-valent iron (nZVI) and the corresponding roles of 1O 2 in degrading pollutants are summarized systematically, chiefly illustrating the mechanisms of persulfate activation to produce 1O 2. The reasons underlying improvements in the degradation of organic pollutants originate from increased generation and enhanced activity of 1O 2 in modified systems and coupling systems based on nZVI. Additionally, in order to figure out how external environment affects the generation and behavior of 1O 2 , several major influence factors are also compared and evaluated. On the whole, this paper draws a relatively clear picture of 1O 2 in the combination of persulfate and nZVI-based systems, opening novel perspective of capitalizing on the merits of 1O 2 to deal with the increasingly troublesome problem of water pollution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Surface-modified bismuth vanadate is prepared for PMS activation under visible light. • CIP oxidation in BVO-2/PMS/Vis system is dominated by 1O 2 and photogenerated holes. • Surface C O acts as Lewis base site to induce PMS hydrolysis in acidic condition. • The efficiently separated electrons can reduce PMS for SO 4 − and OH generation. Lewis basic sites have been shown to induce singlet oxygen (1O 2) generation in metal-free catalysts while have yet to be elucidated in metal-containing bismuth vanadate (BiVO 4). Herein, surface-modified BiVO 4 photocatalysts are developed and applied in peroxymonosulfate (PMS) activation for ciprofloxacin (CIP) abatement employing 1O 2 and photogenerated holes as the primary reactive species. The surface carbonyl moiety acts as Lewis basic sites to induce PMS hydrolysis under acidic conditions for 1O 2 generation. The occurrence of electron transfer from PMS to catalyst accounts for 1O 2 generation via PMS oxidation. Moreover, PMS as an electron acceptor kinetically accelerates charge separation, not only inducing SO 4 − and OH generation but also allowing direct oxidation of CIP by efficiently separated holes. Accordingly, the optimal BVO-2/PMS/Vis system can completely degrade CIP in 9 min under visible light with a reaction rate of 0.4264 min−1, far exceeding the BVO-2/PMS (0.0063 min−1) and BVO-2/Vis (0.0411 min−1) systems. [ABSTRACT FROM AUTHOR]