Boosted photocatalytic decomposition of nocuous organic gases over tricomposites of N-doped carbon quantum dots, ZnFe2O4, and BiOBr with different junctions

TEMPO/O2 Synergistically Mediated BiBrO-Photocatalyzed Decarboxylative Phosphorylation of N-Arylglycines

With both TEMPO and O2 (in air) as the homogeneous redox mediators, BiBrO as the heterogeneous semiconductor photocatalyst, the first example of semi-heterogeneous photocatalytic decarboxylative phosphorylation of N-arylglycines with diarylphosphine oxides was established. A series of α-amino phosphinoxides were efficiently synthesized.

Abatement of microbes and organic pollutants using heterostructural nanocomposites of rice straw CQDs with substituted strontium ferrite

Sustainable use of agricultural waste still remains a challenging task. Herein, we used rice straw as a carbon precursor to prepare carbon quantum dots (CQDs) for photocatalytic applications. Nanocomposites of CQDs with Ti4+ and Mg2+ substituted strontium ferrite (Sr0·4Ti0·4Mg0·2Fe2O4.4) nanoparticles (NPs) in varying w:w ratio was synthesized by ultrasonication method. The successful formation of nanocomposites was confirmed by various microscopic and spectroscopic techniques. The photocatalytic and antibacterial activity of NPs, CQDs and nanocomposites was comparatively evaluated using tetracycline hydrochloride, azure B, Staphylococcus aureus and Escherichia coli as model pollutants. The CQDs-Sr0.4Ti0·4Mg0·2Fe2O4.4 nanocomposite with a w:w ratio of 2:1 showed excellent photocatalytic and antibacterial activity, with the degradation and inactivation efficiency ranging from 97.1% to 99.0% in presence of visible light. The increased specific surface area (117.2 m2/g), and reduction in band gap (2.48 eV-2.09 eV) and decreased photoluminescence intensity of nanocomposites all corroborated these results. The impacting experimental parameters such as catalyst dose, pH and contact time were also examined. Quenching experiments confirmed that hydroxyl radicals (HO∙) radicals and holes (h+) played a vital role in the degradation of pollutants. The kinetics of photodegradation was explained by using the Langmuir-Hinshelwood model. Box-Behnken statistical modelling was used to optimize photocatalytic parameters. Results indicated that the nanocomposite of CQDs with Sr0·4Ti0·4Mg0·2Fe2O4.4 can serve as a promising photocatalyst for the removal of pollutants and microbes.

NCQDs active sites as effective collectors of charge carriers towards enhanced photocatalytic activity of porous Co3O4

In this work, different proportions of N-doped carbon quantum dots/porous Co3O4 (NCQDs/p-Co3O4) NCQDs/Co3O4 composite photocatalysts were prepared by a simple self-assembly method. It was demonstrated by a series of characterizations that 50% NCQDs/Co3O4 has a good visible light response and low electrochemical impedance. The photocatalytic degradation of TC was investigated by the 50% NCQDs/p-Co3O4 composite photocatalyst, and the results showed that the degradation effect of TC reached 81.2% within 120 min. The higher photocatalytic activity of 50% NCQDs/p-Co3O4 was analyzed probably because NCQDs can improve the separation efficiency of photogenerated electron-hole pairs and p-Co3O4 can provide a larger specific surface area and thus has more active sites. This study provides a new strategy for improving the photodegradation activity of Co3O4 photocatalysts.

Enhanced photocarrier separation in Br substitution-induced [W(VI)O6-x] units for highly efficient photocatalytic nitrate reduction under alkaline conditions

Photocatalytic nitrate (NO3-) reduction is considered a promising green and non-polluting technology to solve the nitrate pollution of groundwater and surface water. Herein, a novel Br-substituted Bi2WO6-x ultrathin nanosheets were prepared by a simple hydrothermal method in a strong acid environment containing sixteen alkyl three methyl bromide (CTAB). The catalytic system solves the problems of low carrier separation efficiency, poor performance under alkaline conditions, and a hard-to-activate N = O bond, achieving efficient NO3- removal under alkaline conditions along with high N2 selectivity. It was confirmed that Br-substituted Bi2WO6-x produced the [W(VI)O6-x] units with a strong electron-withdrawing property by changing the polarity of the O-W-O bond. As a result, the effective space charge separation caused by the change of the W valence state and the spontaneous fracture behavior of the N = O bond improved the carriers utilization efficiency and distinctly reduced the reaction energy consumption, synergistically achieving excellent performance.

Shaddock peel-derived N-doped carbon quantum dots coupled with ultrathin BiOBr square nanosheets with boosted visible light response for high-efficiency photodegradation of RhB

In the present work, we constructed a serials of novel shaddock peel-derived N-doped carbon quantum dots (NCQDs) coupled with BiOBr composites. The result showed that the as-synthesized BiOBr (BOB) was composed of ultrathin square nanosheets and flower-like structure, and NCQDs were uniformly dispersed on the surface of BiOBr. Furthermore, the BOB@NCQDs-5 with optimal NCQDs content displayed the top-flight photodegradation efficiency with ca. 99% of removal rate within 20 min under visible light and possessed excellent recyclability and photostability after 5 cycles. The reason was attributed to relatively large BET surface area, the narrow energy gap, inhibited recombination of charge carriers and excellent photoelectrochemical performances. Meanwhile, the improved photodegradation mechanism and possible reaction pathways were also elucidated in detail. On this basis, the study opens a novel perspective to obtain a highly efficient photocatalyst for practical environment remediation.

Significantly activated persulfate by novel carbon quantum dots-modified N-BiOCl for complete degradation of bisphenol-A under visible light irradiation

The practical application of bismuth-based photocatalysts in the field of micropollutant photodegradation is limited due to their weak light absorption and rapid charge recombination. Herein, we have developed a novel carbon quantum dots-modified N-BiOCl (CDs-N-BiOCl) photocatalyst to activate persulfate (PS) for the complete elimination of endocrine-disruptor bisphenol A (BPA) under visible light irradiation. The photoelectric properties characterization shows that N atoms could replace Cl atoms or adsorb on Bi atoms to form local N 1s states in the BiOCl lattice, accompanied by the introduction of doping energy levels that shorten the electron migration distance. Meanwhile, the decorated CDs could effectively accept the photoinduced electrons from N-BiOCl conduction band to facilitate the charge separation. Thus, the 7%CDs-N-BiOCl (7CNB) nanocomposite synergistically activated PS realized rapid and effective degradation of BPA within 20 min (degradation efficiency and mineralization reached 100 % and 66.4 % respectively). Moreover, the 7CNB/PS system displayed favorable adaptability, durability, and interference resistance. Furthermore, the biotoxicity experiments demonstrated that the photodegradation intermediates promoted the growth of Escherichia coli which indicates its eco-friendliness for practical application. Finally, the electron transfer mechanism and the formation of reactive oxygen species in the photodegradation process were interpreted. In short, this work will present a promising strategy for bismuth-based photocatalysts to be used for the efficient treatment of real water bodies under visible light irradiation.

Fabrication of Z-scheme Bi7O9I3/g-C3N4 heterojunction modified by carbon quantum dots for synchronous photocatalytic removal of Cr (Ⅵ) and organic pollutants

Chromium(VI) (Cr(VI)), a highly toxic metal ion, generally co-exists with organic pollutants in industrial effluents. The clean and effective technology for water purification is an imperative issue but still a challenging task. A series of Bi₇O₉I₃/g-C₃N₄ (BOI/CN) composites modified by lignin-derived carbon quantum dots (CQDs) were fabricated by hydrothermal method and applied for synchronous photocatalytic removal of Cr (Ⅵ) and levofloxacin (LEV). With the modification of CQDs in BOI/CN heterojunction, the 0.5-CQD/BOI/CN photocatalyst (0.5% content of CQDs) exhibited stronger light-harvesting capacity, more efficient charge separation, and faster electron transfer. Compared to those of BOI (51.2%), CN (36.8%), and BOI/CN (74.4%), the photoreduction efficiency of Cr(VI) reached up to 100% by 0.5-CQD/BOI/CN under 60 min of light irradiation, together with 94.8% degradation efficiency of LEV. The degradation of LEV was dominantly controlled by active species (•OH and •O₂^-) identified by electron paramagnetic resonance analysis and free radical trapping experiments. The intermediates of LEV were determined by LC-MS and the possible degradation pathway was speculated in combination with density functional theory calculation, involving defluorination, decarboxylation, quinolone rings opening, and piperazine moieties oxidation reactions. This work provides an advanced strategy for the fabrication of high-efficiency CQDs-based Z-scheme photocatalysts for environmental remediation.

Recent Progress of Carbon Dots for Air Pollutants Detection and Photocatalytic Removal: Synthesis, Modifications, and Applications

Rapid industrialization has inevitably led to serious air pollution problems, thus it is urgent to develop detection and treatment technologies for qualitative and quantitative analysis and efficient removal of harmful pollutants. Notably, the employment of functional nanomaterials, in sensing and photocatalytic technologies, is promising to achieve efficient in situ detection and removal of gaseous pollutants. Among them, carbon dots (CDs) have shown significant potential due to their superior properties, such as controllable structures, easy surface modification, adjustable energy band, and excellent electron-transfer capacities. Moreover, their environmentally friendly preparation and efficient capture of solar energy provide a green option for sustainably addressing environmental problems. Here, recent advances in the rational design of CDs-based sensors and photocatalysts are highlighted. An overview of their applications in air pollutants detection and photocatalytic removal is presented, especially the diverse sensing and photocatalytic mechanisms of CDs are discussed. Finally, the challenges and perspectives are also provided, emphasizing the importance of synthetic mechanism investigation and rational design of structures.

Enhanced photocatalytic activity of Fe2O3@ZnO decorated CQD for inactivation of Escherichia coli under visible light irradiation

The present study, magnetically separable Fe₂O₃@ZnO/CQD nanocomposite was successfully prepared via hydrothermal process and characterized with SEM-EDX, XRD, FTIR, VSM and DRS analysis. The effect of operational parameters includes photocatalyst dosage, photocatalyst type, CQD content and Escherichia coli (E. coli) concentration were evaluated on the E. coli inactivation. The disinfecting ability of nanocomposite components was obtained as Fe₂O₃@ZnO/CQD> Fe₂O₃@ZnO> ZnO> Fe₂O₃> CQD which shows a synergetic effect among different components. The highest E. coli inactivation rate (K_max=0.7606 min^-1) was obtained at photocatalyst dosage of 0.2 g/L and 15% CQD content. The MIC and MBC values value for E. coli were determined 0.1172 mg/mL and 0.4948 respectively that the results tests proved the antibacterial functions of the Fe₂O₃@ZnO/CQD. Nanocomposite showed the high reusability after 4 consecutive cycles, K_max decreased from 0.7606 min^-1 to 0.6181 min^-1. Quenching experiments showed ^•OH and h⁺ are the main reactive oxygen species involved in the E. coli inactivation.

Synergetic adsorption and photo-Fenton degradation of methylene blue by ZnFe2O4/SiO2 magnetic double-mesoporous-shelled hollow spheres

Adsorption and Fenton technologies have been widely employed to deal with wastewater. ZnFe₂O₄/SiO₂ magnetic double-mesoporous-shelled hollow spheres (MDSHSs) were feasibly synthesized by a solvothermal method. The as-synthesized MDSHSs show excellent adsorption and selectivity for methylene blue (MB), which it took about only 1 min to reach the adsorption equilibrium. About 50% MB was removed by adsorption, and other 50% MB was degraded under further photo-Fenton process. Effects of experimental conditions on the adsorption and photo-Fenton process were investigated. The mechanisms of MDSHSs formation and photo-Fenton process were proposed. Total organic carbon (TOC) reduction reached as high as 90% with 60 mg/L of MB for 90 min. The experimental results indicated that MDSHSs exhibit a remarkable adsorption and catalytic activity for photo-Fenton process in a wide pH range of 3.3-11.0. Simultaneously, the composite shows an excellent stability and reusability.

Enhanced photocatalytic degradation of glyphosate over 2D CoS/BiOBr heterojunctions under visible light irradiation

Two-dimensional (2D) heterojunction photocatalysts can shorten the carrier transfer pathway. In this study, CoS nanoparticles were deposited on the surface of 2D BiOBr nanosheets to fabricate novel ultrathin and intimate-contact 2D heterojunction photocatalysts by a two-step solvothermal route. Under visible-light (λ > 400 nm) irradiation, the apparent reaction rate constant of glyphosate degradation over 10%CoS/BiOBr reaches 0.0074 min^-1 (74.7% glyphosate was degraded within 3 h), which is about 5.3 times that of pure BiOBr (0.0014 min^-1). The extraordinary photocatalytic performance is attributed to the strong visible-light absorption, the effective charge separation and low charge transfer resistance. The possible photocatalytic reaction process and mechanism over CoS/BiOBr heterojunctions are proposed. Moreover, the 10%CoS/BiOBr sample shows good reusability and stability. This work could provide a new insight for the design and development of 2D heterojunction photocatalysts.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.