With the increasing demands in energy consumption and increasing environmental concerns, it is of vital significance for developing renewable and clean energy sources to substitute traditional fossil ...fuels. As an outstanding candidate, hydrogen is recognized as a green energy carrier due to its high gravimetric energy density, zero carbon footprints, and earth-abundance. Currently, water splitting in alkaline electrolytes represents one of the most promising methods for sustainable hydrogen production, and the key challenge lies in the development of high-performance electrocatalysts for the hydrogen evolution reaction (HER). Given the rapid advances in the design and development of efficient catalysts towards the alkaline HER, especially capable transition metal (TM)-based materials, this review aims to summarise recent progress in the theoretical understanding of the alkaline HER and TM-based electrocatalysts. TM-based catalysts classified by their different anionic compositions (metals, alloys, oxides, hydroxides, sulfides, selenides, tellurides, nitrides, phosphides, carbides, and borides) are comprehensively showcased. Special attention is given to mainstream strategies that can improve the catalytic properties of each category, as well as the underlying structure-activity regimes. Additionally, the challenges for the future development of novel catalysts are also analyzed.
Transition metal-based electrocatalysts for alkaline hydrogen evolution reaction.
Electrocatalytic water splitting (EWS) is a promising route to produce hydrogen in a sustainable and environment-benign manner. To realize the large-scale hydrogen production, it is paramount to ...develop desirable electrocatalysts with engineered structure, high catalytic activity, facile accessibility, low cost, and good durability. Of late, boride-based materials, especially transition-metal borides (TMBs), are emerging as promising candidates for the EWS process. However, so far, little attempt has been made to provide a comprehensive summary on these findings. Herein, this review provides the up-to-date status on upgrading the catalytic performance of TMB-based nanomaterials by regulating the internal and external characteristics. The conventional synthetic techniques are first presented for the preparation of TMB-based catalysts. Afterwards, the advanced strategies are summarized to enhance the catalytic performance of TMBs, including morphology control, component regulation, phase engineering, surface oxidation and hybridization. Then, the design principles of TMB-based electrocatalysts for high-performance EWS are outlined. Lastly, the current challenges and future directions in the development of TMB-based materials are proposed. This review article is expected to envisage insights into the TMBs-based water splitting and to provide strategies for design of the next-generation TMB-based electrocatalysts.
Microplastics have aroused increasing concern as they pose threats to aquatic species as well as human beings. They do not only contribute to accumulation of plastics in the environment, but due to ...absorption they can also contribute to spreading of micropollutants in the environment. Studies indicated that wastewater treatment plants (WWTPs) play an important role in releasing microplastics to the environment. Therefore, effective detection of the microplastics and understanding their occurrence and fate in WWTPs are of great importance towards microplastics control. In this review, the up-to-date status on the detection, occurrence and removal of microplastics in WWTPs are comprehensively reviewed. Specifically, the different techniques used for collecting microplastics from both wastewater and sewage sludge, and their pretreatment and characterization methods are reviewed and analyzed. The key aspects regarding microplastics occurrence in WWTPs, such as concentrations, total discharges, materials, shapes and sizes are summarized and compared. Microplastics removal in different treatment stages and their retention in sewage sludge are explored. The development of potential microplastics-targeted treatment technologies is also presented. Although previous researches in microplastics have undoubtedly improved our level of understanding, it is clear that much remains to be learned about microplastics in WWTPs, as many unanswered questions and thereby concerns still remain; some of these important future research areas are outlined. The key challenges appear to be to harmonize detection methods as well as microplastics mitigation from wastewater and sewage sludge.
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•The detection, occurrence and behavior of microplastics in WWTPs are reviewed.•The collection, pretreatment and characterization of microplastics are analyzed.•The concentrations, materials and properties of microplastics are summarized.•The microplastics removal in WWTPs and retention in sewage sludge are explored.
The atroposelective synthesis of atropisomers with vicinal diaxes remains rare and challenging, due to the steric influence between the two axes and their unique topology. Herein, we disclose a ...single‐step construction of atropisomers with vicinal C−C and C−N chiral diaxes by cyclopentadiene (Cp)‐free cobalt‐catalyzed intramolecular atroposelective C−H annulation, providing the desired diaxial atropisomers of unique structures with decent stereocontrols of both axes (up to >99 % ee and 70 : 1 dr). The optically pure products bearing fluorophores show circular polarized luminescence (CPL) properties, being candidate materials for potential CPL applications. Atropisomerization experiments and density function theory (DFT) calculations are conducted to study the rotational barriers and rotation pathways of the diaxes.
A single‐step construction of atropisomers with vicinal C−C and C−N chiral diaxes by cyclopentadiene (Cp)‐free cobalt‐catalyzed intramolecular atroposelective C−H annulation with decent stereocontrols (up to >99 % ee and 70/1 dr) was reported. Atropisomerization experiments and DFT calculations are done to study the rotational barriers and pathways of the diaxes.
•Autotrophs and heterotrophs in anammox systems are versatile in using organics.•Endogenous organics facilitate biofilm formation and cross-feeding interactions.•19 core and 7 keystone taxa are ...identified based on 149 wastewater anammox samples.•Appropriate organics management is key to enhancing nitrogen removal by anammox.
Anaerobic ammonium oxidation (anammox) represents a promising technology for wastewater nitrogen removal. Organics management is critical to achieving efficient and stable performance of anammox or integrated processes, e.g., denitratation-anammox. The aim of this systematic review is to synthesize the state-of-the-art knowledge on the multifaceted impacts of organics on wastewater anammox community structure and function. Both exogenous and endogenous organics are discussed with respect to their effects on the biofilm/granule structure and function, as well as the interactions between anammox bacteria (AnAOB) and a broad range of coexisting functional groups. A global core community consisting of 19 taxa is identified and a co-occurrence network is constructed by meta-analysis on the 16S rDNA sequences of 149 wastewater anammox samples. Correlations between core taxa, keystone taxa, and environmental factors, including COD, nitrogen loading rate (NLR) and C/N ratio are obtained. This review provides a holistic understanding of the microbial responses to different origins and types of organics in wastewater anammox reactors, which will facilitate the design and operation of more efficient anammox-based wastewater nitrogen removal process.
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The traditional synthesis of ammonia is an industrial process with high energy consumption that is not environmentally friendly; thus, it is urgent to develop cost-effective approaches to synthesize ...ammonia under ambient conditions. In recent years, the photochemical synthesis of ammonia has become a hot research frontier. In this mini review, we summarize the recent advances in materials sciences for photocatalytic nitrogen fixation. Beyond nitrogen fixation, we talk about an alternative for artificial ammonia synthesis and coupling reactions with other reactions for the synthesis of other high-value chemicals. The results and findings of this review will help the development of ammonia synthesis and the synthesis of other high-value chemicals.
The traditional synthesis of ammonia is an industrial process with high energy consumption that is not environmentally friendly; thus, it is urgent to develop cost-effective approaches to synthesize ammonia under ambient conditions.
Biomass is a naturally abundant, sustainable and clean resource, which has potential to replace a portion of the finite petroleum and fossil feedstock for sustainable production of value-added ...chemicals and fuels. However, an efficient conversion process is still difficult to be achieved due to the complex nature of biomass. Currently, the simple, mild, and environmentally benign photocatalytic process appears to be a new research avenue for lignocellulosic biomass transformation. This review provides insights into the state-of-the-art accomplishments in photocatalytic conversion of lignocellulosic biomass and its derivatives, including selective cleavage of dominant bonds of lignin, valorization of processed and native lignin, photoreforming reactions of cellulose and its intermediates, and the depolymerization of robust native lignocellulose under visible or UVA light irradiation. In addition, electricity production from photocatalytic conversion of biomass is also discussed as an innovative lignocellulosic biomass transformation process. We then put forward perspectives for photocatalytic conversion of native lignocellulose and future challenges in increasing the profitability and sustainability of a photocatalysis biorefinery system.
This review summarizes the state-of-the-art accomplishments in photocatalytic conversion of lignocellulosic biomass and its derivatives.
Nitrous oxide (N2O) can be emitted from wastewater treatment contributing to its greenhouse gas footprint significantly. Mathematical modeling of N2O emissions is of great importance toward the ...understanding and reduction of the environmental impact of wastewater treatment systems. This article reviews the current status of the modeling of N2O emissions from wastewater treatment. The existing mathematical models describing all the known microbial pathways for N2O production are reviewed and discussed. These included N2O production by ammonia-oxidizing bacteria (AOB) through the hydroxylamine oxidation pathway and the AOB denitrification pathway, N2O production by heterotrophic denitrifiers through the denitrification pathway, and the integration of these pathways in single N2O models. The calibration and validation of these models using lab-scale and full-scale experimental data is also reviewed. We conclude that the mathematical modeling of N2O production, while is still being enhanced supported by new knowledge development, has reached a maturity that facilitates the estimation of site-specific N2O emissions and the development of mitigation strategies for a wastewater treatment plant taking into the specific design and operational conditions of the plant.
•The models describing all the known microbial pathways for N2O production are reviewed.•The N2O model structures as well as their underlying assumptions are compared.•Model evaluations using lab-scale and full-scale experimental data are discussed.•The key kinetic and stoichiometric parameters are summarized and analysed.•The applicability of these N2O models under various conditions is elucidated.
Microplastics in wastewater inevitably accumulate in waste activated sludge (WAS) via wastewater biological treatment, potentially affecting the subsequent sludge treatment unit. Nevertheless, all ...previous research studies focused on the impacts of the direct addition of one type of model microplastics on the sludge anaerobic treatment process. This approach actually cannot reflect the real situation where multiple different microplastics simultaneously get into the wastewater treatment unit prior to the sludge treatment unit. Herein, this work innovatively proposed a more realistic method to assess the real toxic influences of microplastics on anaerobic WAS fermentation for short-chain fatty acid (SCFA) production by initially adding four typical microplastics (i.e., polyethylene terephthalate, polystyrene, and polypropylene) to the biological wastewater treatment system. Results showed that four microplastics initially entering the biological wastewater treatment reactor had little influence on the subsequent anaerobic SCFA production since WAS solubilization increased but hydrolysis and acidification decreased. In contrast, when the four microplastics were directly dosed in a WAS anaerobic fermenter, although there was no effect on WAS solubilization, the bioprocess of hydrolysis–acidification was clearly suppressed, ultimately significantly (P = 1.86 × 10–7) inhibiting the maximal SCFA production from WAS by 21.5 ± 0.1% compared to the control without microplastic addition. The excessive oxidative stress and toxic leachates from these typical microplastics reduced the relative abundances of key anaerobes (e.g., Longilinea sp.) involved in the anaerobic fermentation. This work revealed that the different pathways of microplastics entering the sludge treatment system had different impacts on anaerobic sludge fermentation processes and selecting a more realistic and accurate approach was important to evaluate the true toxicity of microplastics on the sludge anaerobic treatment system.
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