Water contamination by dyes is a matter of concern for human health and the environment. Various methods (membrane separation, coagulation and adsorption) have been explored to remove/degrade dyes. ...However, now the exploitation of semiconductor assisted materials using renewable solar energy has emerged as a potential candidate to resolve the issue. Although, single component photocatalysts (ZnO, TiO2, ZrO2) were experimented, due to their low efficiency and stability due to the high recombination rate electron-hole pair and inefficient visible light absorption, composites of semiconductor materials are being used. Semiconductor heterojunction systems are developed by coupling two or more semiconductor components. The synergistic effect of their properties, such as adsorption and improved charge carrier migration, is observed to increase overall stability. This review covers recent progress in advanced nanocomposite materials based on g-C3N4, TiO2 and ZnO used as photocatalysts with details of enhancing the photocatalytic properties by heterojunctions, crystallinity and doping. The conclusion at the end displays a summary, research gaps and future outlook. A holistic analysis of recent progress to demonstrate the efficient heterojunctions for photodegradation with optimal conditions, this review will be helpful for the development of efficient heterostructured systems for photodegradation. This review covers references from the year 2017–2020.
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•Mechanistic development in the charge carrier's movement for dye degradation•Graphitic carbon nitride (g-C3N4) TiO2, ZnO based photocatalysts•Improved photocatalysis using heterojunctions, crystal phase and facet, doping
Biosensors have emerged as a potential tool for selective and sensitive detection. Biomolecules like enzymes, deoxyribonucleic acid (DNA), and antibodies are used as recognition sites in biosensors ...due to their high selectivity, sensitivity, and signal-to-noise ratio. Nowadays, biosensors are used to detect many vital biomolecules such as glucose, urea, and cholesterol. Exploiting enzymes for the selective detection of target molecules are very good but may not be easily accomplished as enzymes often need to be immobilized onto support materials, which requests either modifying the surface or using appropriate linkers to synthesize biosensors. Currently, many biosensors’ signal strength and stability still are low, which encourages the fabrication of functionalized nanomaterials/nanoparticles to enhance electrochemical performance. The review covers current progress in modifying enzyme immobilized biosensors to detect biologically essential molecules (glucose, urea, cholesterol). A discussion of the different types of enzyme immobilization is also provided. This review may be helpful for researchers to build rational and novel biosensors for efficient enzyme immobilization and sensing applications.
•Enzyme biosensors generations—first, second, third, current progress.•Enzyme immobilization techniques—electrochemical, chemical, physical.•Enzyme immobilized electrochemical biosensors—glucose, urea, cholesterol.
The “emerging contaminants” (ECs) are predominantly unregulated anthropogenic chemicals that occur in air, soil, water, food, and human/animal tissues in trace concentrations. The ECs are persistent ...in the environment, capable of perturbing the physiology of target receptors and, therefore, are regarded as contaminants of emerging environmental concerns in recent years. The prominent classes of ECs include pharmaceuticals and personal care products (PCPs), surfactants, plasticizers, pesticides, fire retardants, and nanomaterials. Some of the ECs with harmful effects on endocrine systems have been recognized as endocrine disrupting chemicals (EDCs). Since the 1990s intensive research has been done covering environmental occurrence, fate, ecological effects, and treatment technologies of ECs. However, a comprehensive summary of the EC removal techniques, particularly in wastewater treatment plants (WWTPs) are limited. Though the WWTPs are inefficient when it comes to ECs removal, they act as primary barriers against the spread of ECs. Therefore, this paper reviews the treatment technologies currently engaged for ECs removal in WWTPs for further possible upgrades of the existing designs. Results of this review indicate that the fate and distribution of ECs can be approximately estimated based on physicochemical properties like octanol-water partitioning coefficient (e.g., log KOW > 4, maximum sorption potential) and solid-water distribution coefficient e.g., Kd < 300–500 L/kg MLSS (mixed liquor suspended solids), insignificant sorption into sludge. Biodegradation potential of ECs can be predicted from biodegradation constant values (e.g., Kbio < 0.01 = low biodegradation and >10 = high biodegradation). In WWTPs, the EC removal efficiency varies in the range of 20–50%, 30–70%, and >90% during the primary, secondary, and tertiary treatment steps, respectively. Tertiary treatment technologies are considered as the most suitable alternatives for ECs treatment, but complete ECs removal is yet to be achieved. Further advancements in the treatment technologies will unquestionably be necessary in the future.
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•Treatment technologies for emerging contaminants (ECs) are comprehensively reviewed.•The ECs with risk quotient, RQ > 1 have high environmental risk potential.•The ECs with biodegradation kinetics, Kbio > 10 are highly biodegradable in nature.•ASP and MBR are effective biological technologies for ECs removal.•Ozonation and activated carbon treatment are best performing tertiary treatments.
Corrosion is one of the most challenging issues for the large-scale application of magnesium alloys. Fabricating a superhydrophobic surface with a low-cost, easy-to-handle method is meaningful for ...anti-corrosion protection of Mg alloys. In this study, a stearic acid/CeO2 bilayer coating was prepared on AZ31B Mg by a simple electrodeposition method combined with immersion in stearic acid solution. The growth traits of the coating with different electrodeposition current densities and time were evaluated, which demonstrated that 60 min combined with 0.65 mA/cm2 is the optimal electrodeposition condition. Besides, the wettability, anti-corrosion ability, durability, chemical stability and self-cleaning properties of the coating were comprehensively investigated. The results showed that the as-prepared coating exhibited a good superhydrophobic and self-cleaning property with CA>158° and SA<2°. Moreover, the coating demonstrated an improved anti-corrosion performance in 3.5 wt% NaCl solution and was quite stable in the atmosphere and in contact with pH droplets of 1–13.
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•Petal-like hierarchical CeO2 nanosheets were successfully electrodeposited on the AZ31B Mg surface.•Stearic acid/CeO2 bilayer coatings exhibited desirable superhydrophobicity and anticorrosion performance.•As-fabricated superhydrophobic AZ31B Mg was demonstrated excellent chemical stability and abrasion durability.•As-fabricated superhydrophobic AZ31B Mg exhibited good self-cleaning ability.
Second harmonic generation (SHG) and sum frequency spectroscopy (SFS) have provided unique opportunities to probe surfaces and interfaces. They have found broad applications in many disciplines of ...science and technology. In recent years, there has been significant progress in the development of SHG/SFS technology that has significantly broadened the applications of SHG and SFS. In this article, we review the recent progress of the field with emphasis on SFS.
•This is the first study to reveal the microbial structure in rare earth mining soil.•Ionic REEs contents significantly and negatively influenced microbial abundances.•TREEs and ammonium shaped the ...bacterial community in mining soils.•Archaea rather than bacteria were predominantly responsible for ammonia oxidation.
In-situ leaching technology is now widely used to exploit ion adsorption rare earth ore, which has caused serious environmental problems and deterioration of mining soil ecosystems. However, our knowledge about the influences of mining operation on the microbiota in these ecosystems is currently very limited. In this study, diversity and composition of prokaryote and ammonia-oxidizing microorganisms in rare earth mining soil after in-situ leaching practice were examined using quantitative Polymerase Chain Reaction (qPCR) and Illumina high-throughput sequencing. Results showed that in-situ leaching mining considerably impacted microbial communities of the mining soils. The abundances of bacterial, archaeal, and ammonia-oxidizing archaea (AOA) were significantly and negatively correlated with ionic rare earth elements (REEs), while their diversities were relatively stable. Total rare earth elements (TREEs) and ammonium were the strongest predictors of the bacterial community structure, and organic matter was the key factor predicting the variation in the archaeal community. Chloroflexi, Proteobacteria, Acidobacteria, and Actinobacteria were the most abundant bacterial phyla, and archaeal communities were dominated by Thaumarchaeota. Phylogenetic analysis indicated that unclassified Thaumarchaeota and Crenarchaeota were the predominant AOA groups. The non-detection of ammonia-oxidizing bacteria (AOB) and the abundance of AOA indicated that archaea rather than bacteria were predominantly responsible for ammonia oxidation in the mining soil. Network analysis demonstrated that positive interactions among microorganisms could increase their adaptability or resistance to this harsh environment. This study provides a comprehensive analysis of the prokaryotic communities and functional groups in rare earth mining soil after mining operation, as well as insight into the potential interactive mechanisms among soil microbes.
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•C. sorokiniana-activated sludge improved nutrients removal in the dark.•Consortium consumed less O2 than activated sludge.•Photosynthetic ability of algae was reserved in the dark ...despite oxidative stress.•Performance order: light consortium > dark consortium > activated sludge.•Interaction associated with cofactors, vitamins, terpenoids and polyketides.
Light limitation often occurs in algae-bacteria consortium. Chlorella sorokiniana is special for heterotrophic growth in the dark, autotrophic or mixotrophic growth in the light. Wastewater treatment by Chlorella sorokiniana-activated sludge consortium under dark heterotrophic conditions (24 h dark, dark period of 12 h/12 h light/dark) was systematically evaluated for the first time. The performance closely depended on sludge/algae ratio with best initial ratio of 1:2 (R2). Compared to activated sludge (R0), R2 showed enhanced NH4+-N and P removal (by 6% and 10%, respectively), similar COD removal, and better settleability. Notably, less O2 consumption of R2 than activated sludge made energy-saving possible. Further analysis found that interaction made sludge/algae ratio reversal to be 3:1. The promoting interaction between algae and bacteria was associated with up-regulated cofactors and vitamins, while defensive interaction came from secondary metabolites of terpenoids and polyketides. Despite oxidative stress in the dark consortium, photosynthesis of algae reactivated when switched into light. The performance order was light consortium > dark consortium > activated sludge. Nitrosomonas and Dechloromonas were enriched for nutrients removal. The results reveal the superiority of algae-bacteria consortium over activated sludge whether with or without light.
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•Microwave enhanced arsenic selective leaching from smelter dusts in alkali media.•98 % of As was removed through microwave-assisted leaching process.•Energy cost was cut down to ...one-tenth of the conventional leaching process.•Moderate alkali concentration is feasible.•Thermodynamic and kinetic mechanisms for As leaching were proposed.
Alkaline sulphide leaching processes have been widely used for the arsenic selective removal from metallurgical wastes. However, high consumption of energy and chemicals as well as long extraction time have forced the industries to find more cost-effective and eco-friendly separation techniques. In this work, a feasible microwave-enhanced leaching process was developed for arsenic selective removal from copper smelter dusts, and arsenic leaching efficiency could reach ∼98 % after leaching for 10 min with 0.5 mol·L−1 alkaline solution, in contrast to 86 % removal for the conventional electrical-heating leaching with even a more intensive alkali content (1.0 mol·L−1) and a longer extract time (1.5 h). Furthermore, energy cost was cut down to one-tenth of the conventional leaching process. Two enhancing mechanisms were proposed: 1) rapid oxidation of As(III) of the dusts occurred under microwave irradiation reduced the energy potential for arsenic dissolving in alkali media; 2) cracks and fissures formed in the dust particles after microwave, coupled with the temporary and localized superheating in the bulk liquid, would dramatically enhance arsenic leaching kinetics and decrease the activation energy value from 42.88 to 35.81 kJ·mol−1 (40–70 ℃). This work may have important implications to the development of new technologies to purify arsenic-bearing materials.
Nanoscale zero-valent iron (nZVI) has been extensively used to remove various pollutants. However, the rapid deactivation due to aggregation and surface passivation severely limits its practical ...application. In this study, a novel composite with nZVI supported by pinecone biochar (nZVI-PBC) was successfully synthesized and used for the removal of high concentration Cr(VI) from aqueous solution in the presence of Shewanella oneidensis MR-1 (MR-1). The results showed that the nZVI-PBC coupling with MR-1 (nZVI-PBC/MR-1) exhibited an excellent removal performance for high concentration Cr(VI) compared to the nZVI-PBC alone. Under optimal conditions, 100 mg/L Cr(VI) could be removed completely by nZVI-PBC/MR-1 within 48 h, while only 39.50% of Cr(VI) was removed by nZVI-PBC alone. The improvement of Cr(VI) removal is due to the dissolution of the surface passivation layer of nZVI-PBC, formation of sorbed Fe(II) in the presence of MR-1, and an important role of extracellular polymeric substance (EPS) derived from MR-1. X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near-edge structure spectra (XANES) confirmed that most Cr(VI) was reduced to insoluble Cr(III) and formed Cr2O3, CrxFe1-x(OH)3 and FeCr2O4 precipitates, and a small amount of unreduced Cr(VI) was immobilized through adsorption and complexation. The results suggest that nZVI-PBC/MR-1 can effectively overcome the limitations of nZVI and achieve highly efficient removal of high concentration Cr(VI).
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•nZVI-PBC coupling with MR-1 exhibited an excellent capacity for Cr(VI) removal.•Sorbed Fe(II) could act as a strong reductant to reduce Cr(VI) to Cr(III).•The EPS derived from MR-1 play an important role in Cr(VI) removal.•nZVI-PBC coupling with MR-1 overcomes the aggregation and passivation of nZVI.•The mechanism of Cr(VI) removal by nZVI-PBC coupling with MR-1 was proposed.
Metal-organic frameworks (MOFs) have emerged as promising materials and have attracted researchers due to their unique chemical and physical properties—design flexibility, tuneable pore channels, a ...high surface-to-volume ratio that allow their distinct application in diverse research fields—gas storage, gas separation, catalysis, adsorption, drug delivery, ion exchange, sensing, etc. The rapidly growing CO2 in the atmosphere is a global concern due to the excessive use of fossil fuels in the current era. CO2 is the prime cause of global warming and should be ameliorated either through adsorption or conversion into value-added products to protect the environment and mankind. Nowadays, MOFs are exploited as a photocatalyst for applications of CO2 reduction. Since the use of semiconductors limits the use of visible light for photocatalytic reduction of CO2, MOFs are promising options. The current review describes recent development in the application of MOFs as host, composites, and their derivatives in photocatalytic reduction of CO2 to CO and different organic chemicals (HCOOH, CH3OH, CH4). Efficient charge separation and visible light absorption by incorporation of active sites for efficient photocatalysis have been discussed. The selection of material for high CO2 uptake and potential strategies for the rational design and development of high-performance catalysts are outlined. Major challenges and future perspectives have also been discussed at the last of the review.
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•The applications of MOFs as host, composites, and their derivatives.•Photocatalytic reduction of CO2 to CO and different organic chemicals.•Incorporation of active sites for efficient charge separation and visible light absorption.•The rational design and development of high-performance catalysts.
