In this study, Fe3O4/sepiolite composites as peroxymonosulfate (PMS) catalysts were successfully synthesized via a simple water bath method for tetracycline (TC) degradation. The results indicated that the composite with 70% Fe3O4 loading amount exhibited the highest TC degradation efficiency (90.12%), and its reaction rate constant (0.02193 min−1) was around 2.07 times higher than that of pure Fe3O4. The enhanced catalytic activity was mainly attributed to the uniform deposition of Fe3O4 nanoparticles with smaller grain size (17.24 nm) on sepiolite, leading to the larger specific surface area (120.61 m2/g) and more exposed reaction active sites. The electron paramagnetic resonance (EPR) and quenching experiments displayed that 1O2 species played the predominant roles in TC degradation process. Besides, potential catalytic mechanisms and degradation pathways of TC were proposed. The toxicity of TC was reduced during the degradation process. Overall, this work can provide a new strategy for the rational design of promising mineral-based PMS catalyst for the wastewater treatment. 

Improved PMS activation by natural sepiolite/Fe3O4 composite for effective tetracycline degradation: Performance, mechanism and degradation pathway

Effect of aged nanoscale zero-valent iron amendment and capping on phosphorus mobilization in sediment

Dual Z-scheme heterojunction with highly separation efficiency of photoinduced carriers and outstanding redox capability has received considerable attention and hold great promise for environmental remediation. Herein, magnetic dual Z-scheme g-C3N4/ZnFe2O4/Ag2CO3 heterojunction was successfully constructed, and applied as a dual-function photocatalyst for tetracycline (TC) degradation and bacterial inactivation. The optimized g-C3N4/ZnFe2O4/Ag2CO3 heterojunction exhibited excellent photocatalytic capacity for TC degradation with a rate constant of 0.0154 min−1, which is 2.73, 3.08, and 2.92 times higher compared to that of the g-C3N4, ZnFe2O4, and g-C3N4/ZnFe2O4, respectively. Impressively, the g-C3N4/ZnFe2O4/Ag2CO3-1.25 heterojunction displayed satisfying activity within a wider range of pH (3.0–9.0), TC concentration (5–25 mg L−1), and with the addition of various anions including Cl-, HCO3-, SO42-, and NO3-. Meanwhile, 6.5-log of Escherichia coli cells could also be inactivated by g-C3N4/ZnFe2O4/Ag2CO3-1.25 heterojunction under visible light. Mechanism exploration based on trapping experiment, electron paramagnetic resonance (EPR) analysis, and liquid chromatography-mass spectrometer (LC-MS) indicated that the improved photocatalytic performance resulted from the synergetic effect of semiconductors and constructed dual Z-scheme heterojunction, which significantly promotes charge separation rate and endows strong redox capacity. As expected, the toxicity of TC degradation intermediates was reduced according to the Toxicity estimation analysis based on a quantitative structure activity relationships (QSAR) method. Further, the g-C3N4/ZnFe2O4/Ag2CO3 heterojunction also demonstrated magnetic separation property and satisfactory photocatalytic stability even after 4 cycles. This work offers a new perspective on constructing novel magnetic dual Z-scheme heterojunction with dual-function photocatalytic properties and is of significance for water remediation. 

Construction of novel dual Z-scheme g-C3N4/ZnFe2O4/Ag2CO3 heterojunction with enhanced visible-light-driven performance for tetracycline degradation and bacterial inactivation

Phosphate recovery from water and wastewater serves as a feasible alternative to the exploitation of scarce phosphate rock resources. Currently, phosphate is recovered using adsorption-based techniques due to their desirable features, such as a low running cost, feasible operation, and high efficiency. Clay minerals (CMs), a group of earth-abundant resources, have attracted increasing interest in phosphate management. However, because the surface and crystal lattice of CMs are negatively charged, CMs are inefficient and have been replaced with cost-effective modified CMs (mCMs). This review comprehensively covers the current advances in mCM-mediated phosphate recovery. We first discussed the crystal features of natural CMs and the diverse techniques used for mCMs to enhance their phosphate-removal capacity. Subsequently, we covered the processes of mCM-driven phosphate management, namely, ion exchange, hydrogen bonding, crystallization, Lewis acid-base interactions, electrostatic interactions, precipitation, and electrostatic-ligand exchange. Further assessments revealed that mCMs can efficiently remove phosphate through multiple synergistic mechanisms. This review also discussed the effects of anions, humic acids, and cations on the mCMs management of phosphate and analyzed mCMs applications in various water environments, specifically, phosphate passivation materials in lake sediments and the phosphate management of municipal/seawater wastewater. We examined the reutilization of phosphate-loaded mCMs in agriculture from a circular economy perspective, and finally discussed the commercial application prospects of mCMs in environmental pollution remediation, which may help to avert the global phosphate-resource crisis and improve wastewater management. 

Comprehensive review of modified clay minerals for phosphate management and future prospects

Synthesis of few-layer carbon nitride with wide absorption spectra is an interesting research area. Heteroatom doping, particularly sulfur (S) doping, can effectively prevent band gap widening triggered by the quantum confinement effect in nanoscale carbon nitride sheets. Herein, different from that in second calcination sulfuration, the presulfuration supramolecular precursors can in situ form the S-doped carbon nitride (SCN) nanosheet stacked microrods. This few-layer frame construction possesses a large specific surface area (139.06 m2 g−1), exposes more active sites, and facilitates the internal reflection of photons. Furthermore, the introduction of S distorts the conjugated structure of the original heptazine ring, narrowing the band gap of carbon nitride through the activation of the n→π⋆ transition in valence band electrons. Consequently, the light absorption range is extended to 700 nm. Finally, the hydrogen evolution rate of SCN0.8 (3925.8 µmol g−1 h−1) is 8.1 times that of bulk carbon nitride (485.2 µmol g−1 h−1) under simulated sunlight conditions (AM 1.5G). The stacking of sheets avoids the accumulation of nanosheets and enhances performance and structural stability. The proposed structure aims to maximize the utilization of synergistic effects of heteroatom doping and morphology regulation to improve photocatalytic hydrogen evolution. Furthermore, this work provides a new perspective for the multidimensional synchronous optimization of photocatalysts. 

硫掺杂氮化碳纳米片棒状聚集体用于光催化析氢

Herein, a new type of peroxymonosulfate (PMS) activator—phosphorus-doped carbon nitride (P-C3N4)—was prepared using a one-step thermal shrinkage method. Material characterisation confirmed the successful doping of phosphorus in graphite-phase carbon nitride (g-C3N4) by replacing the carbon atoms in its triazine ring structure to form PN bonds. Phosphorus doping can regulate and re-organise the surface electronic structure of g-C3N4 without changing its structure. Moreover, phosphorus doping promotes varying degrees of optimisation of the g-C3N4 pore structure and electronic transport between the g-C3N4 sites. Batch experiments on tetracycline (TC) degradation revealed that 0.2 P-C3N4 showed the best physicochemical properties, the constructed P-C3N4/PMS system exhibited high TC removal efficiency and P-C3N4 exhibited good reusability and structural stability. Quenching experiments and electron paramagnetic resonance tests revealed that singlet oxygen was the primary active species in the P-C3N4/PMS system. The mechanism of PMS activation using P-C3N4 was then proposed. The analysis of TC and its intermediate products using liquid chromatography–mass spectroscopy demonstrated that TC was primarily degraded via ring-opening, hydroxylation, deamination and dealkylation reactions. Analysis using the toxicity estimation software tool demonstrated that most intermediate products were less toxic than TC. Thus, this study provides a feasible method for removing TC from aquatic environments. 

Phosphorus doping to enhance the peroxymonosulfate activation efficiency of carbon nitride for degrading tetracycline

In this study, oxygen-doped carbon nitride (O–C3N4) was prepared by thermal polymerization and was applied to activate peroxymonosulfate (PMS) for tetracycline (TC) degradation. Experiments were performed to comprehensively evaluate the degradation performance and mechanism. The oxygen atom replaced the nitrogen atom of the triazine structure, which improves the specific surface area of the catalyst, enriches the pore structure and achieves higher electron transport capacity. The characterization results showed that 0.4 O–C3N4 had the best physicochemical properties, and the degradation experiments showed that the 0.4 O–C3N4/PMS system had a higher TC removal rate in 120 min (89.94%) than the unmodified graphitic-phase C3N4/PMS system (52.04%). Cycling experiments showed that O–C3N4 has good reusability and structural stability. Free radical quenching experiments showed that the O–C3N4/PMS system had free radical and non-radical pathways for TC degradation and that the main active species was singlet oxygen (1O2). Intermediate product analysis showed that TC was mineralized to H2O and CO2 mainly by the ring opening, deamination, and demethylation reactions. The results of this study show that the 0.4 O–C3N4/PMS system is simple to prepare and is efficient at removing TC from contaminated water.

Tetracycline degradation mechanism of peroxymonosulfate activated by oxygen-doped carbon nitride

Organic matter was increased due to the input of plant litter, resulting in changes in the physicochemical properties and enhancement of greenhouse gas (GHG) emissions in water bodies. There are few reports on effects of decomposition of aquatic plants on GHGs emissions. This study investigated the effects of the degradation of two aquatic plants, Potamogeton crispus and Typha orientalis Presl, upon release of CO2 and CH4 at the sediment–water interface. During early decomposition, the release of CO2 and CH4 at the sediment–water interface was increased by the degradation of the two aquatic plants, and release flux of CO2 and CH4 were increased rapidly at first and then decreased. Due to the differences in properties of C, lignin, cellulose and other components of the plants, the Potamogeton crispus group obtained higher abundance of genes relevant to CO2 and CH4 metabolism, which leads to the increase of CO2 and CH4 emissions compared with that of the Typha orientalis Presl. In addition, dissolved oxygen and pH were decreased due to the decomposition of organic matter in the plant residues at the sediment–water interface, resulting in growth of anaerobic microorganisms. The increase of the relative abundance of anaerobic microorganisms promoted the decomposition of organic matter in the sediment and the enhancement of cell respiration, promoting the release of CH4 and CO2 during the decomposition of aquatic plants. 

Effects of Decomposition of Submerged Aquatic Plants on CO2 and CH4 Release in River Sediment–Water Environment

Phosphorus (P) inactivation agents have been widely used to control sediment P release for combating lake eutrophication. The settlement and decomposition of algal biomass from the overlying water can alter the microenvironment of the capping layer and potentially affect the performance of P inactivation agents. In this study, we explored the impacts of algal decomposition on the performance of lanthanum/aluminum comodified attapulgite (LAA), a commonly used P inactivation agent, and the underlying mechanisms through incubation experiments. The results showed that algal settlement and decomposition could inactivate LAA. After algal settlement, the amount of P locked in the LAA decreased by 11.8% relative to the control. Algal decomposition induced anoxia in the capping layer of LAA, which favored the growth of phosphate-solubilizing bacteria, thereby enhancing P release; meanwhile, driven by algal decomposition, more organic matter penetrated the capping layer and competed with P adsorption sites. The increased desorption ability and decreased adsorption ability inhibited the performance of LAA, increasing the P permeability of the capping layer. This study provides beneficial information for future field applications of P inactivation agents for lake restoration. 

/pdf/algal-settlement-inactivates-lanthanum-aluminum-comodified-lw44ynbw.pdf

Algal Settlement Inactivates Lanthanum/Aluminum Comodified Attapulgite: Implications for Phosphorus Control in Shallow Lakes

The spatial distribution and characterization of phosphorus and nitrogen in a water-carrying lake: a case study of Lake Jiaogang, China

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