UV-light-induced photocatalytic performance of reusable MnFe-LDO–biochar for tetracycline removal in water

A review of the degradation of antibiotic contaminants using advanced oxidation processes: modification and application of layered double hydroxides based materials

In recent years, the treatment of organic pollutants has become a global concern due to the threat to human health posed by emerging contaminants, especially antibiotic contamination. Advanced oxidation processes (AOPs) can solve the organic pollution problem well, which have been identified as a promising solution for the treatment of hard-to-handle organic compounds including antibiotic contaminants. Layered double hydroxides (LDHs) are excellent catalysts because of their flexible tunability, favorable thermal stability, abundant active sites, and facile exchangeability of intercalated anions. This paper conducted a systematic review of LDHs-based materials used for common antibiotic removal by three significant AOP technologies, such as photocatalysis, the Fenton-like processes, and peroxymonosulfate catalysis. The degradation effects studied in various studies were reviewed, and the mechanisms were discussed in detail based on the type of AOPs. Finally, the challenges and the application trends of AOPs that may arise were prospected. The aim of this study is to suggest ways to provide practical guidance for the screening and improvement of LDH materials and the rational selection of AOPs to achieve efficient antibiotic degradation. This could lead to the development of more efficient and environmentally friendly materials and processes for degrading antibiotics, with significant implications for our ecological conservation by addressing water pollution.

Domain-limited thermal transformation preparation of novel graphitized carbon-supported layered double oxides for efficient tetracycline degradation

The resource utilization of industrial lignin to construct high-performance catalysts for wastewater treatment field is pioneering research. Herein, the novel graphitized carbon-supported CuCoAl-layered double oxides (LDOs-GC) were successfully designed by the domain-limited thermal transformation technology using sodium lignosulfonate (LS) self-assembled CuCoAl-layered double hydroxides as the precursor. The optimized LDOs-GC catalyst owned the excellent tetracycline (TC) degradation of 98.0% within 15 min by activated peroxymonosulfate (PMS) under optimal conditions (20 mg/L catalyst, 1.5 mM PMS, 30 mg/L TC). The density of metal ions in the catalyst and the synergistic interaction between graphitized carbon (GC) and metal ions played a major role in TC degradation. Based on a comprehensive analysis, the TC degradation in LDOs-GC/PMS system was proved to be accomplished by a combination of free radicals (SO4·- and HO·) and non-radicals (1O2). Meanwhile, the possible degradation pathways of TC were proposed by the analysis of TC degradation intermediates and a comprehensive analysis of the rational reaction mechanism for TC degradation by LDOs-GC/PMS system was also performed. This work provides a new strategy for developing novel high-performance catalysts from industrial waste, while offering a green, cheap and sustainable approach to antibiotic degradation.

Ag2S Nanoparticles Supported on 3D Flower-Shaped Bi2WO6 Enhanced Visible Light Catalytic Degradation of Tetracycline

A three-dimensional flower-shaped Bi2WO6 has been prepared by a hydrothermal procedure without the addition of an auxiliary agent and under neutral conditions with ultrapure water serving as solvent, and the Ag2S-Bi2WO6 composite with weight ratios of 5, 10, and 15% was prepared by a hydrothermal method. The crystallinity, morphology, mode of binding, and optical properties of the Ag2S-Bi2WO6 composite were characterized, the results of which showed that the composite had excellent dispersion, crystallinity, and purity. The composite with a weight ratio of 10% had the best photocatalytic performance, and the degradation rate of tetracycline reached 95.51% within 120 min, an increase of 27.35% over Bi2WO6. In experiments, some focus was given to the effect of the initial solution pH and the concentrations of humic acid and inorganic anions on the degradation efficiency. Based on free radical capture experiments and the semiconductor theory, the main active substances and mechanisms in the optical catalytic reaction process were studied, and speculation was given concerning the degradation pathway for the target pollutants. This study has conceived novel methods for the development of dual semiconductor systems consisting of a Ag NP composite and in doing so has provided new approaches for the development and photocatalysis for water pollution control.

Enhancing the Photocatalytic Performance of Antibiotics Using a Z-Scheme Heterojunction of 0D ZnIn2S4 Quantum Dots and 3D Hierarchical Inverse Opal TiO2

Limited light absorption and rapid photo-generated carriers' recombination pose significant challenges to the practical applications of photocatalysts. In this study, we employed an efficient approach by combining the slow-photon effect with Z-scheme charge transfer to enhance the photo-degradation performance of antibiotics. Specifically, we incorporated 0D ZnIn2S4 quantum dots (QDs) into a 3D hierarchical inverse opal (IO) TiO2 structure through a facile one-step process. This combination enhanced the visible light absorption and provided abundant active surfaces for efficient photo-degradation. Moreover, the ZnIn2S4 QDs formed an artificial Z-scheme system with IO-TiO2, facilitating the separation and migration of charge carriers. To achieve a better band alignment with IO-TiO2, we doped Ag into the ZnIn2S4 QDs (Ag: ZIS QDs) to adjust their energy levels. Through an investigation of the different Ag contents in the ZnIn2S4 QDs, we found that the optimal photo-degradation performance was achieved with Ag (2.0): ZIS QDs/IO-TiO2, exhibiting degradation rates 19.5 and 14.8 times higher than those of ZnIn2S4 QDs and IO-TiO2, respectively. This study provides significant insights for elevating the photocatalytic capabilities of IO-TiO2 and broadening its prospective applications.

Biochar/layered double hydroxides composites as catalysts for treatment of organic wastewater by advanced oxidation processes: A review

Heterogeneous advanced oxidation process has been widely studied as an effective method for removing organic pollutants in wastewater, but the development of efficient catalysts is still challenging. This review summaries the present status of researches on biochar/layered double hydroxides composites (BLDHCs) as catalysts for treatment of organic wastewater. The synthesis methods of layered double hydroxides, the characterizations of BLDHCs, the impacts of process factors influencing catalytic performance, and research advances in various advanced oxidation processes are discussed in this work. The integration of layered double hydroxides and biochar provides synthetic effects for improving pollutant removal. The enhanced pollutant degradation in heterogeneous Fenton, sulfate radical-based, sono-assisted, and photo-assisted processes using BLDHCs have been verified. Pollutant degradation in heterogeneous advanced oxidation processes using BLDHCs is influenced by process factors such as catalyst dosage, oxidant addition, solution pH, reaction time, temperature, and co-existing substances. BLDHCs are promising catalysts due to the unique features including easy preparation, distinct structure, adjustable metal ions, and high stability. Currently, catalytic degradation of organic pollutants using BLDHCs is still in its infancy. More researches should be conducted on the controllable synthesis of BLDHCs, the in-depth understanding of catalytic mechanism, the improvement of catalytic performance, and large-scale application of treating real wastewater.

Metal-organic framework-based nanomaterials as opto-electrochemical sensors for the detection of antibiotics and hormones: A review

Increasing trace levels of antibiotics and hormones in the environment and food samples are concerning and pose a threat. Opto-electrochemical sensors have received attention due to their low cost, portability, sensitivity, analytical performance, and ease of deployment in the field as compared to conventional expensive technologies that are time-consuming and require experienced professionals. Metal-organic frameworks (MOFs) with variable porosity, active functional sites, and fluorescence capacity are attractive materials for developing opto-electrochemical sensors. Herein, the insights into the capabilities of electrochemical and luminescent MOF sensors for detection and monitoring of antibiotics and hormones from various samples are critically reviewed. The detailed sensing mechanisms and detection limits of MOF sensors are addressed. The challenges, recent advances, and future directions for the development of stable, high-performance MOFs as commercially viable next-generation opto-electrochemical sensor materials for the detection and monitoring of diverse analytes are discussed.

Bismuth-based nanostructured photocatalysts for the remediation of antibiotics and organic dyes

A serious threat to human health and the environment worldwide, in addition to the global energy crisis, is the increasing water pollution caused by micropollutants such as antibiotics and persistent organic dyes. Nanostructured semiconductors in advanced oxidation processes using photocatalysis have recently attracted a lot of interest as a promising green and sustainable wastewater treatment method for a cleaner environment. Due to their narrow bandgaps, distinctive layered structures, plasmonic, piezoelectric and ferroelectric properties, and desirable physicochemical features, bismuth-based nanostructure photocatalysts have emerged as one of the most prominent study topics compared to the commonly used semiconductors (TiO₂ and ZnO). In this review, the most recent developments in the use of photocatalysts based on bismuth (e.g., BiFeO₃, Bi₂MoO₆, BiVO₄, Bi₂WO₆, Bi₂S₃) to remove dyes and antibiotics from wastewater are thoroughly covered. The creation of Z-schemes, Schottky junctions, and heterojunctions, as well as morphological modifications, doping, and other processes are highlighted regarding the fabrication of bismuth-based photocatalysts with improved photocatalytic capabilities. A discussion of general photocatalytic mechanisms is included, along with potential antibiotic and dye degradation pathways in wastewater. Finally, areas that require additional study and attention regarding the usage of photocatalysts based on bismuth for removing pharmaceuticals and textile dyes from wastewater, particularly for real-world applications, are addressed.

Degradation of organic pollutants from water by biochar-assisted advanced oxidation processes: Mechanisms and applications

Biochar has shown large potential in environmental remediation because of its low cost, large specific surface area, porosity, and high conductivity. Biochar-assisted advanced oxidation processes (BC-AOPs) have recently attracted increasing attention to the remediation of organic pollutants from water. However, the effects of biochar properties on catalytic performance need to be further explored. There are still controversial and knowledge gaps in the reaction mechanisms of BC-AOPs, and regeneration methods of biochar catalysts are lacking. Therefore, it is necessary to systematically review the latest research progress of BC-AOPs in the treatment of organic pollutants in water. In this review, first of all, the effects of biochar properties on catalytic activity are summarized. The biochar properties can be optimized by changing the feedstocks, preparation conditions, and modification methods. Secondly, the catalytic active sites and degradation mechanisms are explored in different BC-AOPs. Different influencing factors on the degradation process are analyzed. Then, the applications of BC-AOPs in environmental remediation and regeneration methods of different biochar catalysts are summarized. Finally, the development prospects and challenges of biochar catalysts in environmental remediation are put forward, and some suggestions for future development are proposed.

Application of biochar-based photocatalysts for adsorption-(photo)degradation/reduction of environmental contaminants: mechanism, challenges and perspective

The fast increase of population results in the quick development of industry and agriculture. Large amounts of contaminants such as metal ions and organic contaminants are released into the natural environment, posing a risk to human health and causing environment ecosystem problems. The efficient elimination of contaminants from aqueous solutions, photocatalytic degradation of organic pollutants or the in-situ solidification/immobilization of heavy metal ions in solid phases are the most suitable strategies to decontaminate the pollution. Biochar and biochar-based composites have attracted multidisciplinary interests especially in environmental pollution management because of their porous structures, large amounts of functional groups, high adsorption capacities and photocatalysis performance. In this review, the application of biochar and biochar-based composites as adsorbents and/or catalysts for the adsorption of different contaminants, adsorption-photodegradation of organic pollutants, and adsorption-(photo)reduction of metal ions are summarized, and the mechanism was discussed from advanced spectroscopy analysis and DFT calculation in detail. The doping of metal or metal oxides is the main strategy to narrow the band gap, to increase the generation and separation of photogenerated e−-h+ pairs, to produce more superoxide radicals (·O2−) and hydroxyl radicals (·OH), to enhance the visible light absorption and to increase photocatalysis performance, which dominate the photocatalytic degradation of organic pollutants and (photo)reduction of high valent metals to low valent metals. The biochar-based composites are environmentally friendly materials, which are promising candidates in environmental pollution cleanup. The challenge and perspective for biochar-based catalysts are provided in the end.

Graphical Abstract

Photo-Induced Holes Initiating Peroxymonosulfate Oxidation for Carbamazepine Degradation via Singlet Oxygen

Peroxymonosulfate (PMS) has been intensively used to enhance the photocatalytic activity of catalysts, which is adopted as an electron acceptor to inhibit the recombination of electrons and holes. However, the effect of holes generated by visible light (VL) on PMS activation is always overlooked. Herein, the VL/Bi2WO6/PMS process was constructed for the efficient removal of organics, in which the degradation rate of carbamazepine (CBZ) increased by over 33.0 times by the introduction of PMS into Bi2WO6 under visible light. The radical quenching and determination experiments confirmed that the photogenerated holes could firstly oxidize PMS to form SO5•− and react with HSO5− to produce 1O2, then inducing the formation of other reactive species to greatly enhance the performance of pollutant removal by the VL/Bi2WO6/PMS process. Density functional theory (DFT) predicted that sites with high Fukui index (f0) on CBZ were more susceptible to being attacked, resulting in hydroxylation, ring closure, and C=C bond cleavage of CBZ. Toxicity estimation indicated that photocatalysis degradation products from CBZ were less toxic compared to the parent compound. This study provides a potential avenue for improving photocatalytic efficiency and widening the application of photocatalytic technology in wastewater purification.

Efficient removal of antibiotic in single and binary mixture of nickel by electrocoagulation process: Hydrogen generation and cost analysis

In discharged water, antibiotics and heavy metals frequently coexist, forming stable and recalcitrant complexes. Environmental concerns about how to efficiently treat this type of pollution are growing. Using Fe and Al electrodes, electrocoagulation (EC) was applied to remove tetracycline (TC) as a single pollutant as well as TC-nickel ions in a binary mixture from water. The effects of critical variables and the TC-Ni molar ratio (1:1, 1:2, and 2:1) were studied. The Fe electrode achieved 99.3% TC removal after 60 min in a single pollutant system containing 15 mgL^-1 of TC, while the Al electrode achieved 99.8% removal in 20 min at optimal conditions. The EC process demonstrated excellent electrodegradation efficiency towards TC-Ni complexes. When the TC to Ni²⁺ ratio was 1:1 and 1:2, respectively, TC elimination was 100% in 10 min and 99.6% in 20 min. We noted that a sufficient amount of Ni²⁺ could increase TC decomposition by electrocatalysis. The amount of hydrogen gas produced after treatment of a 0.2 L TC solution alone is 22.2-13.99 mol m^-3, whereas it was 27.2-40.8 mol m^-3 in the TC-Ni binary mixture, which can generate more than 35% of the electrical energy needed to power the EC system. To evaluate the generated sludge, FTIR analysis was performed.

Single and combined effects of antibiotics and nanoplastics from surgical masks and plastic bottles on pathogens

Over the last decade, pollution of plastics and antibiotics has increased in its threat to the environment and human health. However, very limited information is available concerning impact of co-presence of plastics and antibiotics on environment and human health. Moreover, the potential ingestion and inhalation of nano(micro)plastics due to the disposable materials has dramatically increased. With the outbreak and spread of the COVID-19 in the world, disposable surgical masks and plastic bottles have been widely used by the public, and their rapid use and improper dispensing can cause to increase plastic pollution risk on human. However, impacts of co-presence of nano(micro)plastics and antibiotics on pathogens have yet been demonstrated. Therefore, this study aims to investigate the impact the individual and combined influences of nano-sized plastics (surgical mask and plastic bottles) and antibiotics (amoxicillin and spiramycin) towards the main susceptible bacterium (Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa) by microbial activity, biofilm formation and their biochemical characteristics. The results showed that antimicrobial efficiencies of the tested antibiotics were reduced (approximately 10-98%) with the plastics. Moreover, the biochemical pathways of the microbial activity changed by the plastics entrance. Polymer structure and sorption play the role on the reduction in the inhibition of pathogens. In the meantime, the biofilm formation changed and characteristic of the extracellular polymeric substance with the co-presence of plastics and antibiotics mostly depended on the polymer structure, exposure time and sorption.

Degradation of tetracycline by FeNi-LDH/Ti3C2 photo-Fenton system in water: From performance to mechanism

Recently, photo-Fenton technology has been widely used to degrade tetracycline (TC) because of its great efficiency and wide application range. Herein, Fe-Ni layered double hydroxides (FeNi-LDH)/Ti₃C₂ photo-Fenton system was constructed in this study. The results showed the introduction of Ti₃C₂ solved some problems of FeNi-LDH such as poor conductivity, easy aggregation, and high recombination rate of photoelectron. Benefiting from these advantages, FeNi-LDH/Ti₃C₂ exhibited excellent TC removal rate of 94.7% while pure FeNi-LDH was only 54%. Besides, FeNi-LDH/Ti₃C₂ possessed strong pH tolerance (2-11) and the removal efficiency was still up to 82% after the four-cycle experiment. Furthermore, the quenching experiments revealed the reaction mechanism, where ∙OH and ·O₂^- were the primary active radicals for degrading TC. Last, the results of the simulated wastewater treatment and the inorganic ion interference tests showed that FeNi-LDH/Ti₃C₂ possessed practical application potential. In brief, this study shows that FeNi-LDH/Ti₃C₂ can offer a certain theoretical basis for the actual development of hydrotalcite in heterogeneous photo-Fenton systems.

A Comprehensive Review of Layered Double Hydroxide-Based Carbon Composites as an Environmental Multifunctional Material for Wastewater Treatment

As is well known, hydrotalcite-like compounds, such as layered-double-hydroxide (LDH) materials, have shown great potential applications in many fields owing to their unique characteristics, including a higher anion exchange capacity, a structure memory effect, low costs, and remarkable recyclability. While the lower surface area and leaching of metal ions from LDH composites reduce the process efficiency of the catalyst, combining LDH materials with other materials can improve the surface properties of the composites and enhance the catalytic performance. Among organic compounds, carbon materials can be used as synergistic materials to overcome the defects of LDHs and provide better performance for environmental functional materials, including adsorption materials, electrode materials, photocatalytic materials, and separation materials. Therefore, this article comprehensively reviews recent works on the preparation and application of layered double-hydroxide-based carbon (LDH–C) composites as synergistic materials in the field of environmental remediation. In addition, their corresponding mechanisms are discussed in depth. Finally, some perspectives are proposed for further research directions on exploring efficient and low-cost clay composite materials.

Hydrothermal Carbonization of Waste Sugarcane Bagasse for the Effective Removal of Emerging Contaminants from Aqueous Solution

Porous carbon spheres were fabricated from sugarcane bagasse using a sustainable hydrothermal carbonization process followed by alkali impregnation inert atmosphere activation. Developed spheres were technically analysed for their chemical science, structural morphology, texture, porosity with respect to size distribution, and thermal degradation. Spheres are functionally enriched with oxygenated groups showing amorphous nature portraying as a smooth surface. After activation, intensity of functional groups is reduced due to reduction reaction by KOH thereby yielding highly rich porous carbon. The active surface area developed on spheres is 111 m2 g-1 holding pores that are mesoporous in nature. Resistance to thermal exposure using TGA showed that decomposition of hemicelluloses followed by cellulose yielded aromatized carbon-rich skeleton through thermal degradation of carboxyl and hydroxyl groups. Developed carbon was found to be effective in removing Ciprofloxacin Hydrochloride from water with maximum adsorption capacity of 110.008 mg g-1. Mechanistic removal followed pseudo-second-order kinetics along with Freundlich mode of adsorption. The presence of carboxylic and hydroxyl groups in porous carbon favoured elimination of CPF from water. The development of HTC-derived carbon helped conserving the energy thereby reducing the cost requirement.

Application of Magnetic Composites in Removal of Tetracycline through Adsorption and Advanced Oxidation Processes (AOPs): A Review

Water pollution induced by the tetracycline (TC) has caused global increasing attention owing to its extensive use, environmental persistence, and potential harm for human health. Adsorption and advanced oxidation processes (AOPs) have been promising techniques for TC removal due to ideal effectiveness and efficiency. Magnetic composites (MCs) which exploit the combined advantages of nano scale, alternative sources, easy preparation, and separation from wastewater are widely used for catalysis and adsorption. Herein, we intensively reviewed the available literature in order to provide comprehensive insight into the applications and mechanisms of MCs for removal of TC by adsorption and AOPs. The synthesis methods of MCs, the TC adsorption, and removal mechanisms are fully discussed. MCs serve as efficient adsorbents and photocatalysts with superior performance of photocatalytic performance in TC degradation. In addition, the TC can be effectively decomposed by the Fenton-based and SO4•− mediated oxidation under catalysis of the reported MCs with excellent catalytic performance. Based on the existing literature, we further discuss the challenge and future perspectives in MCs-based adsorption and AOPs in removing TC.

CuCr2O4@CaFe-LDO photocatalyst for remarkable removal of COD from high-strength olive mill wastewater

Wastewater from the olive mill constitutes a serious environmental concern, as it is characterized by a high inorganic and organic load. Here, a hybrid photocatalyst based on calcined Ca-Fe-LDH was successfully synthesized for the degradation of phenolic compounds and the removal of chemical oxygen demand (COD) from the high-strength olive mill wastewater (OMW). The catalyst (CuCr₂O₄@CaFe-LDO) displayed a stable ~4.48 µA cm^-2 photocurrent response, a 2.56 eV bandgap and a wide variety of pores with an average size of 12.51 nm. 1.0 g CuCr₂O₄@CaFe-LDO achieved 66% COD removal after 300 mins without an oxidant in the dark, while after 180 mins of reaction, CuCr₂O₄@CaFe-LDO/K₂S₂O₈/sunlight system resulted in ~99% and 98.3% COD and colour removal. Seven phenolic compounds were found in the crude OMW, with hydroxytyrosol (76.84%) and tyrosol (15.14%) being the main ones. The final pH of the sample treated increased from 4.3 to 7.3, which confirmed the degradation of phenolics and fatty acids in the OMW. OH, SO₄^-, h⁺ and O₂^- contributed notably to the degradation of polyphenols and the spent catalyst was easily and rapidly recovered from the bulk solution due to its saturation magnetization of 54.7 emu g^-1.