Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review

Tannic Acid-Decorated Bimetallic Copper-Gold Nanoparticles with High Catalytic Activity for the Degradation of 4-Nitrophenol and Rhodamine B

In this study, tannic acid (TA) was applied as a stabilizing agent for synthesizing bimetallic copper-gold (CuAu) nanoparticles. Cu(NO3)2 and NaAuCl4 were used as the sources of copper and gold ions, respectively, and NaBH4 was employed as a reducing agent. The prepared TA-CuAu nanoparticles were extensively characterized via ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction, and zeta potential analyses. To evaluate their catalytic activity, the TA-CuAu nanoparticles and NaBH4 were applied in the degradation of 4-nitrophenol (4-NP) and rhodamine B (RB) individually and in a mixture. The individual degradation of 4-NP and RB was completed within 10 min, and the apparent rate constants were calculated as 0.3046 and 0.2628 min-1, respectively, emphasizing the efficient catalytic activity of the TA-CuAu nanoparticles. Additionally, controlled experiments were performed for the degradation of 4-NP and RB in the absence of catalysts or NaBH4 to investigate the kinetic feasibility of the catalytic reactions. A mixture of 4-NP and RB was successfully degraded within 10 min using the TA-CuAu nanoparticles as catalysts. Furthermore, the reuse of the catalysts after five successive cycles demonstrates an outstanding performance with no significant loss in the catalytic activity. Finally, the successful treatment of the tap and lake water samples spiked with 4-NP and RB using the TA-CuAu nanoparticles further confirmed their application potential as catalysts in environmental water remediation.

Advanced applications of hydroxyapatite nanocomposite materials for heavy metals and organic pollutants removal by adsorption and photocatalytic degradation: A review

This comprehensive review delves into the forefront of scientific exploration, focusing on hydroxyapatite-based nanocomposites (HANCs) and their transformative role in the adsorption of heavy metals (HMs) and organic pollutants (OPs). Nanoscale properties, including high surface area and porous structure, contribute to the enhanced adsorption capabilities of HANCs. The nanocomposites' reactive sites facilitate efficient contaminant interactions, resulting in improved kinetics and capacities. HANCs exhibit selective adsorption properties, showcasing the ability to discriminate between different contaminants. The eco-friendly synthesis methods and potential for recyclability position the HANCs as environmentally friendly solutions for adsorption processes. The review acknowledges the dynamic nature of the field, which is characterized by continuous innovation and a robust focus on ongoing research endeavors. The paper highlights the HANCs' selective adsorption capabilities of various HMs and OPs through various interactions, including hydrogen and electrostatic bonding. These materials are also used for aquatic pollutants' photocatalytic degradation, where reactive hydroxyl radicals are generated to oxidize organic pollutants quickly. Future perspectives explore novel compositions, fabrication methods, and applications, driving the evolution of HANCs for improved adsorption performance. This review provides a comprehensive synthesis of the state-of-the-art HANCs, offering insights into their diverse applications, sustainability aspects, and pivotal role in advancing adsorption technologies for HMs and OPs.

Degradation of pharmaceuticals and other emerging pollutants employing bi-metal catalysts/magnesium and/or (green) hydrogen in aqueous solution

Contaminations by pharmaceuticals, personal care products, and other emerging pollutants in water resources have become a seriously burgeoning issue of global concern in the first third of the twenty-first century. As societal reliance on pharmaceuticals continues to escalate, the inadvertent introduction of these substances into water reservoirs poses a consequential environmental threat. Therefore, the aim of this study was to investigate reductive degradation, particularly, catalytic hydrogenation regarding model pollutants such as diclofenac (DCF), ibuprofen (IBP), 17α-ethinylestradiol (EE2), or bisphenol-A (BPA), respectively,  in aqueous solutions at lab scale. Iron bimetals (zero valent iron, ZVI, and copper, Cu, or nickel, Ni) as well as zero valent magnesium (Mg, ZVM) in combination with  rhodium, Rh, or palladium, Pd, as hydrogenation catalysts (HK), were investigated. Studies were executed through various short-term batch experiments, with multiple sample collections, over a total range of 120 min. The results indicated that DCF was attenuated at over 90 % when exposed to Fe-Cu or a Fe-Ni bimetal (applied as a single model pollutant). However, when DCF was part of a mixture alongside with IBP, EE2, and BPA, the attenuation efficacy decreased to 79 % with Fe-Cu and 23 % with Fe-Ni. Conversely, both IBP and BPA exhibit notably low attenuation levels with both bimetals, less than 50 %, both deployed as single substances or in mixtures. No reaction (degradation) products could be identified employing LC-MS, but sometimes a release of the parent pollutant when applying an acetic acid buffer could be noted to a certain extent, suggesting adsorption processes on corrosion products such as iron hydroxide and/or oxides. Surprisingly, Mg in combination with Rh (Rh-HK) or Pd (Pd-HK) showed a significantly rapid decrease in the concentrations of DCF, EE2, and BPA, in part up to approximately 100 %, that is, within a few minutes only in part due to hydrogenation degradation reactions (related reaction products could actually be identified by LC-MS; adsorption processes were not observed here). Moreover, kinetic modeling of the DCF degradation with Mg-Rh-HK was conducted at different temperatures (15 °C, 20 °C, 25 °C, 35 °C) and varied initial concentrations (2.5 mg/L, 5.0 mg/L, 7.5 mg/L, 10.0 mg/L). The outcomes prove that the degradation of DCF at the Rh-HK's surface followed a modified first-order kinetics, most probably by catalytic hydrodehalogenation and subsequent hydrogenation of the aromatic moieties (molecular hydrogen was provided by the corrosion of Mg). From the determined reaction rate constants at four different temperatures, the activation energy was estimated to be 59.6 kJ/mol by means of the Arrhenius equation what is in good agreement with similar results reported in the literature. This coupled hydrodehalogenation and hydrogenation approach may be upscaled into a new promising technical process for comprehensively removing such pharmaceuticals and similar pollutants in sewage plants in a single step, furthermore, even in combination with adsorption by activated carbon and/or ozonation which have already been established at some sewage plants in Switzerland and Germany recently.

Cold plasma turns mixed-dye-contaminated wastewater bio-safe

The excessive and uncontrollable discharge of diverse organic pollutants into the environment has emerged as a significant concern, presenting a substantial risk to human health. Among the advanced oxidation processes used for the purification of wastewater, cold plasma technology is superior in fast and effective decontamination but often fails facing mixed pollutants. To address these issues, here we develop the new conceptual approach, plasma process, and proprietary reactor that ensure, for the first time, that the efficiency of treatment (114.7%) of two mixed organic dyes, methylene blue (MB) and methyl orange (MO), is higher than when the two dyes are treated separately. We further reveal the underlying mechanisms for the energy-efficient complete degradation of the mixed dyes. The contribution of plasma-induced ROS and the distinct degradation characteristics and mechanism of pollutants in mixed treatment are discussed. The electron transfer pathway revealed for the first time suggest that the mixed pollutants reduce the overall redox potentials and facilitate electron transfer during the plasma treatment, promoting synergistic degradation effects. The integrated frameworks including both direct and indirect mechanisms provide new insights into the high-efficiency mixed-contaminant treatment. The degradation products for mixed degradation are revealed based on the identification of intermediate species. The plasma-treated water is proven safe for living creatures in waterways and sustainable fishery applications, using in vivo zebrafish model bio-toxicity assay. Overall, these findings offer a feasible approach and new insights into the mechanisms for the development of highly-effective, energy-efficient technologies for wastewater treatment and reuse in agriculture, industry, and potentially in urban water networks.

Pyto-Architechture of Ag, Au and Ag-Au bi-metallic nanoparticles using waste orange peel extract for enable carcinogenic Congo red dye degradation

Ecologically inspired to develop silver, gold and silver/gold bimetallic nanoparticles from discarded orange peel extract. The plant-derived compounds included in discarded orange peel extract have been accountable for the development of Ag, Au and Ag-Au bimetallic nanoparticles, that might be used in the biosynthetic process. The qualitative assessment of developed silver, gold and silver/gold bimetallic nanoparticles has been performed by UV-visible, XRD pattern, FT IR analysis, TEM/HRTEM, EDX and BET isotherm analysis. In this investigation, the photocatalytic effect of developed silver, gold and silver/gold bimetallic nanoparticles on Congo red dye breakdown efficiency was achieved at 96%, 94%, and 99.2%, respectively. Due to prolonged electron-hole recombination process was investigated using UV irradiation and reused for up to 5 consecutive runs without significant loss of photocatalytic activity. Moreover, silver, gold, and silver/gold bimetallic nanoparticles manufactured in an environmentally benign manner could potentially contribute to the ecological cleanup.

Sugeno fuzzy inference system modeling and DFT calculations for the treatment of pesticide-laden water by newly developed arginine functionalized magnetic Mn-based metal organic framework

The uncontrolled utilization of pesticides poses a significant risk to the environment and human health, making its management essential. In this regard, a new arginine functionalized magnetic Mn-based metal-organic framework (Arg@m-Mn-MOF) was fabricated and assessed for the removal of cypermethrin (CYP) and chlorpyrifos (CHL) from aqueous system. The Arg@m-Mn-MOF was characterized by scanning electron microscopy, energy dispersive X-ray, Fourier transform infrared spectroscopy, X-ray diffraction, and Brunauer-Emmett-Teller analysis. Various parameters were optimized in a series of batch experiments and the following conditions were found optimal: pH: 4 and 5, contact time: 20 min, adsorbent dosage: 0.6 and 0.8 g L-1 with initial concentration: 10 mg L-1 and temperature: 298 K for CYP and CHL, respectively. The composite attained a maximum removal capacity of 44.84 and 71.42 mg g-1 for CYP and CHL, respectively. The elucidated data was strongly fitted to the pseudo-second-order model of kinetics (R2 > 0.98) and Langmuir isotherm (R2 > 0.98). Based upon 350 experimental datasets obtained from batch studies and interpolated data, the adsorption capacity of the adsorbent was elucidated with R2 > 0.97 (CHL) and > 0.91 (CYP). The adsorption energy (- 11.67 kcal mol-1) calculated by Gaussian software suggests a good interaction between arginine and CHL through H-bonding. The present study's findings suggested the prepared Arg@m-Mn-MOF as a promising adsorbent for the efficient removal of pesticides from agriculture runoff.

Fabrication of an in situ-grown TiO2 nanowire thin film and its enhanced photocatalytic activity

TiO₂ is a promising photocatalyst used in practical environmental remediation. TiO₂ photocatalysts are usually implemented in two forms: suspended powder and immobilized thin films. A simple technique for fabricating TiO₂ thin film photocatalyst was developed in this work. The fabricated TiO₂ thin film photocatalyst featured a homogeneous nanowire layer grown in situ on the parent Ti plate. The optimized fabrication protocol was to soak the ultrasonically cleaned and acid-washed Ti plate in 30% H₂O₂ solution containing 3.2 mM melamine and 0.29 M HNO₃ at 80 °C for 72 h and then anneal at 450 °C for 1 h. TiO₂ nanowires with uniform diameters were homogeneously arrayed on the Ti plate surface. The thickness of the TiO₂ nanowire array layer was 1.5 μm. The pore properties of the TiO₂ thin film were close to those of P25. The band gap of the fabricated photocatalyst was 3.14 eV. The photocatalytic activity of the fabricated photocatalyst toward 10 mg/L RhB and 1 mg/L CBZ demonstrated greater than 60% degradation under 2 h UVC irradiation. The RhB and CBZ degradation efficiencies remained at a good level after 5 consecutive cycles. Mechanical wearing, such as 2 min sonication, will not lead to significant suppression of the photocatalytic activity. Photocatalytic RhB and CBZ degradation using the fabricated photocatalyst favored an acidic > alkaline > neutral environment. The presence of Cl^- slightly suppressed the photocatalytic degradation kinetics. However, RhB and CBZ photocatalytic degradation kinetics were promoted in the copresence of SO₄^2- or NO₃^-.

Doping rare earth cations with an additional chemical reduction synergistically weakened the photocatalytic performance of ceria

Chemical reducing or rare earth cations (RE) doping was normally employed to promote the photocatalytic performance of ceria, aimed to evaluate their cooperation influences, ceria was obtained by decomposing homogenously RE (RE = La, Sm, and Y)-doped CeCO₃OH in H₂. XPS and EPR results evidenced that the excess oxygen vacancies (OVs) were formed in RE-doped CeO₂ compared to the un-doped ceria. However, all the RE-doped ceria unexpectedly showed an impeded photocatalytic activity towards to methylene blue (MB) photodegradation. The 5% Sm-doped ceria had the best MB photodegradation ratio of 81.47% after 2-h reaction in all RE-doped samples, which was lower than that of 87.24% for the un-doped ceria. After doping RE cations and chemical reducing, the band gap of ceria were almost narrowed, while the PL spectra and photo-electro characterizations indicated that the separation efficiency of photo-excited e^-/h⁺ (electrons/holes) was reduced. The RE dopants and formed excess OVs including inner and surface OVs was proposed to promote the recombination of e^-/h⁺ which further hindered the generation of active species of ·O₂^- and ·OH, and finally weakened the photocatalytic activity of ceria.

Removal of ceftriaxone sodium antibiotic from pharmaceutical wastewater using an activated carbon based TiO2 composite: Adsorption and photocatalytic degradation evaluation

The water pollution becomes a serious concern for the sustainability of ecosystems due to the existence of pharmaceutical products (ceftriaxone (CEF) antibiotic). Even in low concentration of CEF has lethal effects on ecosystem and human health. To remove CEF, TiO₂ is considered as an effective and efficient nanoparticles, however its performance is reduced due to wider energy gap and rapid recombination of charge carriers. In this study, activated carbon based TiO₂ (ACT-X) heterogeneous nanocomposites were synthesized to improve the intrinsic properties of TiO₂ and their adsorption-photocatalytic performance for the removal of CEF. The characterization results revealed that ACT-X composites have slower recombination of charge carriers, lower energy band gap (3.05 eV), and better light absorption under visible region of light. From ACT-X composites, the ACT-4 photocatalyst has achieved highest photocatalytic degradation (99.6%) and COD removal up (99.2%). The results of radical scavengers showed that photocatalytic degradation of CEF is mainly occurred due to superoxide and hydroxyl radicals. Meanwhile, the reusability of ACT-4 up to five cycles shows more than 80% photocatalytic degradation, which make the process more economical. The highest experimental adsorption capacity is achieved up to 844.8 mg g^-1 using ACT-4. The favorable and multilayer heterogeneous adsorption is carried out according to the well-fitted data with pseudo-second-order and Freundlich models, respectively. These results indicate that the carbon-based TiO₂ composites can be used as a green, stable, efficient, effective, reusable, renewable, and sustainable photocatalyst to eliminate the pharmaceutical pollutants (antibiotics) via adsorption and photocatalytic degradation processes.

Preparation of MnO2-Carbon Materials and Their Applications in Photocatalytic Water Treatment

Water pollution is one of the most important problems in the field of environmental protection in the whole world, and organic pollution is a critical one for wastewater pollution problems. How to solve the problem effectively has triggered a common concern in the area of environmental protection nowadays. Around this problem, scientists have carried out a lot of research; due to the advantages of high efficiency, a lack of secondary pollution, and low cost, photocatalytic technology has attracted more and more attention. In the past, MnO₂ was seldom used in the field of water pollution treatment due to its easy agglomeration and low catalytic activity at low temperatures. With the development of carbon materials, it was found that the composite of carbon materials and MnO₂ could overcome the above defects, and the composite had good photocatalytic performance, and the research on the photocatalytic performance of MnO₂-carbon materials has gradually become a research hotspot in recent years. This review covers recent progress on MnO₂-carbon materials for photocatalytic water treatment. We focus on the preparation methods of MnO₂ and different kinds of carbon material composites and the application of composite materials in the removal of phenolic compounds, antibiotics, organic dyes, and heavy metal ions in water. Finally, we present our perspective on the challenges and future research directions of MnO₂-carbon materials in the field of environmental applications.

Biomimetic Catalysts Based on Au@TiO2-MoS2-CeO2 Composites for the Production of Hydrogen by Water Splitting

The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO₂ nanowires (TiO₂NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS₂ nanosheets, and CeO₂ nanoparticles (CeO₂NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS₂ and CeO₂NPs in the catalyst substantially improved the H₂ production, with values of ca. 1114 μm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H₂ from water.

Two dimensional S-scheme Bi2WO6-TiO2-Ti3C2 nanocomposites for efficient degradation of organic pollutants under natural sunlight

Two-dimensional (2D) materials have fascinated the researchers to exploit their properties including large surface area, ability to act as a support and to form face-to-face interfacial contact with other 2D materials for fabricating efficient photocatalytic materials. In this work, Bi₂WO₆, TiO₂ and Ti₃C₂ nanosheets have been used synthesizing different series of binary Bi₂WO₆-TiO₂ and ternary Bi₂WO₆-TiO₂-Ti₃C₂ 2D nanocomposites by an electrostatic self-assembly synthesis route. The as-prepared pristine materials and binary and ternary nanocomposites were characterized by different structural, morphological and compositional characterization techniques to confirm their successful synthesis and 2D morphology. It was found that the optimized Bi₂WO₆-TiO₂ (20 wt%) and Bi₂WO₆-TiO₂ (20 wt%)-Ti₃C₂ (5 wt%) nanocomposites showed 97.0% and 98.5% degradation of methyl green in 80 min and 40 min, respectively, which was higher than their pristine counterparts. The enhanced activity was credited to the large surface area offered by 2D nanocomposites, pollutant adsorption and enhanced photogenerated charge separation and transfer facilitated by S-scheme mechanism and face-to-face interfacial contact of different components of these nanocomposites. This work delivers an example of highly efficient 2D nanocomposites and discusses the role of Ti₃C₂ as an electron acceptor in S-scheme photocatalytic system.

New bismuth oxyiodide/chitosan nanocomposite for ultrasonic waves expedited adsorptive removal of amoxicillin from aqueous medium: kinetic, isotherm and thermodynamic investigations

Amoxicillin (AMX) is a widely used antibiotic, which induces harmful effects to nature via bioaccumulation and persistence in the environment if discharged untreated into water bodies. In the current study, a novel bionanocomposite, bismuth oxyiodide-chitosan (BiOI-Ch), was synthesized by a facile precipitation method and its amoxicillin (AMX) adsorption capacity in the presence of ultrasonic waves has been explored. Multiple batch experiments were performed to achieve the optimum operational parameters for maximum adsorption of AMX and the obtained results were as follows: pH 3, 80 mg g^-1 AMX concentration, 1.7 g L^-1 adsorbent dose, temperature 298 K and ultrasonication time 20 min. Composite removed approximately 90% AMX from the solution under optimized conditions, while the maximal adsorption capacity was determined to be 81.01 mg g^-1. BiOI-Ch exhibited superior adsorption capacity as compared to pure BiOI (33.78 mg g^-1). To understand the dynamics of reaction, several kinetic and isotherm models were also examined. The adsorption process obeyed pseudo-second-order kinetic model (R² = 0.98) and was well fitted to Freundlich isotherm (R² = 0.99). The addition of biowaste chitosan to non-toxic bismuth-based nanoparticles coupled with ultrasonication led to enhanced functional groups as well as surface area of the nanocomposite resulting in superior adsorption capacity, fast adsorption kinetics and improved mass transfer for the removal of AMX molecules. Thus, this study demonstrates the synergistic effect of ultrasonication in improved performance of novel BiOI-Ch for potential application in the elimination of persistent and detrimental pollutants from industrial effluent after necessary optimization for large-scale operation.

Accurate data prediction by fuzzy inference model for adsorption of hazardous azo dyes by novel algal doped magnetic chitosan bionanocomposite

A bionanocomposite comprising of magnetic chitosan doped with algae isolated from native habitat was fabricated and utilized as an efficient adsorbent for the removal of hazardous azo dyes, namely, Direct Red 31 (DR31) and Direct Red 28 (DR28). The algal doped magnetic chitosan (Alg@mCS) was comprehensively characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction analysis (XRD), and Brunauer-Emmett-Teller (BET). On the sorption of dyes, the influence of various process variables such as pH, adsorbent dosage, contact time, temperature, and initial dyes concentration were addressed. The adsorbent demonstrated maximal removal of DR31 and DR28 at pH 5 and 3, respectively. The maximum adsorption capacity of DR31 and DR28 was observed at Alg@mCS dose of 0.6 g L^-1 and 7 g L^-1 in 10 and 20 min, respectively. The Redlich Peterson isotherm model was shown to be appropriate for dye adsorption, indicating monolayer coverage of the dyes on the adsorbent surface (R² > 0.99). The adsorption process followed pseudo-second-order kinetics (R² > 0.99). Based on 320 experimental datasets from batch studies and interpolated data, adaptive neuro-fuzzy inference system (ANFIS) models were utilized to estimate dye elimination (percent). A number of parameters were calculated to validate the model's applicability. The Alg@mCS was proven to be a useful adsorbent for eliminating toxic and harmful azo dyes from aqueous solutions.

TiO2-immobilized porous geopolymer composite membrane for removal of antibiotics in hospital wastewater

This experimental research proposes an environment-friendly and low-cost porous geopolymer composite membrane (PGCM) to treat antibiotics in hospital wastewater. The proposed PGCM consisted of two layers: a porous support layer and a dense coating layer. The dense coating layer was synthesized by incorporating variable TiO₂ content (0, 2, 6, and 10 wt%) into the geopolymer matrix. The dense coating layer was of hierarchical mesoporous structure with 700 μm in thickness and adhered to the porous support layer. The average pore size, total pore volume, and open porosity of the dense coating layer decreased with an increase in TiO₂, resulting in reduced water permeability. The PGCM was applied to remove six target antibiotics including amoxicillin, ciprofloxacin, norfloxacin, sulfamethoxazole, tetracycline, and trimethoprim in real hospital wastewater. By comparison, the PGCM with 10 wt% TiO₂ achieved the highest antibiotic removal efficiencies, with the adsorption and combined adsorption/photodegradation removal efficiencies for the target antibiotics of 38-75% and 74-86%, respectively. The novelty of this research lies in the use of a tailor-made porous geopolymer composite membrane incorporated with TiO₂ photooxidation as a single-step treatment of recalcitrant antibiotics contained in hospital wastewater.

A sustainable remediation of Congo red dye using magnetic carbon nanodots and B. pseudomycoides MH229766 composite: mechanistic insight and column modelling studies

In the present investigation, a biocomposite, magnetic carbon nanodot immobilized Bacillus pseudomycoides MH229766 (MCdsIB) was developed and consequently characterized using SEM-EDX, FTIR, XRD, and VSM analyses to effectively biotreat hazardous Congo red (CR) dye present in water bodies. The adsorptive efficiency of MCdsIB for the detoxification of CR from wastewater was investigated both in batch and column schemes. Optimum batch parameters were found as pH 3, 50 mg L-1 dye concentration, 150 min equilibrium time, and 2 g L-1 MCdsIB dosage. The Freundlich isotherm model best fit the experimental data, and the maximum adsorption capacity of MCdsIB was observed as 149.25 mg g-1. Kinetic data were in accordance with the pseudo-second-order model where the adsorption rate reduced with the rise in the initial concentration of dye. Intra-particle diffusion was discovered as the rate-limiting step following 120 min of the adsorption process. Furthermore, despite being used continually for five consecutive cycles, MCdsIB demonstrated excellent adsorption capacity (> 85 mg g-1), making it an outstanding recyclable material. The CR dye was efficiently removed in fixed-bed continuous column studies at high influent CR dye concentration, low flow rate, and high adsorbent bed height, wherein the Thomas model exhibited an excellent fit with the findings acquired in column experiments. To summarize, the current study revealed the effectiveness of MCdsIB as a propitious adsorbent for CR dye ouster from wastewater.

The photocatalytic activity and purification performance of g-C3N4/carbon nanotubes composite photocatalyst in underwater environment

Graphite carbon nitride (g-C₃N₄) is a promising photocatalyst for its high catalytic activity, low-cost and high-biosafety characteristics. Due to the complexity of underwater photochemical reaction conditions and the disadvantages of g-C₃N₄ itself such as low specific surface area, easy recombination of photogenerated electron-hole pairs and insufficient light absorption capacity, the application of g-C₃N₄ in the field of water purification is limited. For improving underwater photocatalytic performance of g-C₃N₄, a g-C₃N₄/carbon nanotubes (CNT-CN) composite photocatalyst with high specific surface area and enhanced light absorption capacity were prepared by in situ solvothermal method. Its photodegradation efficiency at different underwater transmission light was further studied. The results show that CNT has good compatibility with g-C₃N₄. g-C₃N₄ can grow in situ on the surface of CNT and form a stable composite structure. Moreover, its degradation efficiency under long-wavelength irradiation is improved significantly. The degradation rate of CNT-CN at 550-700 nm was about 3 times than that of g-C₃N₄. Furthermore, CNT-CN can maintain higher photocatalytic activity under water. At 40 cm depth where light intensity and ultraviolet spectra were attenuated 63.8% and 80.1%, respectively, the degradation rate of CNT-CN3 can still reach 3.49 times than that of g-C₃N₄. Based on this study, the introduction of CNT effectively promotes the electron-hole separation efficiency of g-C₃N₄, widens its spectral response range, and thus improves its underwater degradation efficiency.

The state-of-the-art development of photocatalysts for the degradation of persistent herbicides in wastewater

Herbicides are one of the most recurring pollutants in the aquatic system due to their widespread usage in the agriculture sector for weed control. Semiconductor-based photocatalysts have gained recognition due to their ability to degrade and mineralize pollutants into harmless by-products completely. Lately, many studies have been done to design photocatalysts with efficient separation of photogenerated charge carriers and enhanced light absorption. Photocatalyst engineering through doping with metal and non-metal elements and the formation of heterojunction are proven effective for minimizing the recombination of electron-hole pairs and enlarging the absorption in the visible light region. This review focuses on discussing and evaluating the recent progress in the types of photocatalysts and their performance in the remediation of herbicides in wastewater. The development of innovative hybrid technologies is also highlighted. The limitations and challenges of photocatalysis technology in the present literature have been identified, and future studies are recommended.

Ultrasonication expedited As(III) adsorption onto chitosan impregnated Ni-Fe layered double hydroxide biosorbent: Optimization studies and artificial intelligence modelling

Chitosan intercalated Ni-Fe layered double hydroxide (Ni-Fe LDH/Ch), prepared by co-precipitation was examined for adsorptive elimination of arsenic (III). Energy Dispersive X-ray analysis, X-ray diffraction, Fourier Transform Infrared spectroscopy, Scanning Electron Microscopy, and Dynamic Light Scattering validated the successful synthesis of the composite with enhanced adsorption sites. Maximal As(III) removal was obtained at adsorbent dose 1 gL^-1, pH 7, ultrasonication time 30 min, temperature 298 K, and initial arsenic concentration 50 mgL^-1. The experimentally obtained values fit the Langmuir isotherm and pseudo-second-order dynamics well (R² > 0.98), while thermodynamic evaluation confirmed exothermic and spontaneous reaction (ΔG = -8.13 kJ mol^-1). Further, adaptive neuro-fuzzy inference system and artificial neural network successfully predicted As(III) removal percentage with a high correlation coefficient (R² > 0.94) and low statistical errors (MSE< 0.002, AARE< 0.063). The prepared material successfully brought down arsenic level by 62% in a natural water sample and showed good reusability up to 5 consecutive treatment cycles. The results recommended that Ni-Fe LDH/Ch has ample potential for arsenic remediation, and further investigations can be carried out for large-scale applications.

Carbon-based nanocomposite materials with multifunctional attributes for environmental remediation of emerging pollutants

Carbon-based materials are among the most biosynthesized nanocomposites with excellent tunability and multifunctionality features, that other materials fail to demonstrate. Naturally occurring materials, such as alginate (Alg), can be combined and modified by linking the active moieties of various carbon-based materials of interest, such as graphene oxide (GO), carbon nanotubes (CNTs), and mesoporous silica nanocomposite (MSN), among others. Thus, several types of robust nanocomposites have been fabricated and deployed for environmental remediation of emerging pollutants, such as pharmaceutical compounds, toxic dyes, and other environmentally hazardous contaminants of emerging concern. Considering the above critiques and added features of carbon-based nanocomposites, herein, an effort has been made to spotlight the synergies of GO, CNTs, and MSN with Alg and their role in mitigating emerging pollutants. From the information presented in this work, it can be concluded that Alg is a material that has excellent potential. However, its use still requires further tests in different areas and other materials to carry out a holistic investigation that exploits its versatility for environmental remediation purposes.

Co3O4 Nanopetals Grown on the Porous CuO Network for the Photocatalytic Degradation

Designing a novel photocatalytic composite for the efficient degradation of organic dyes remains a serious challenge. Herein, the multi-layered Co₃O₄@NP-CuO photocatalyst with unique features, i.e., the self-supporting, hierarchical porous network as well as the construction of heterojunction between Co₃O₄ and CuO, are synthesized by dealloying-electrodeposition and subsequent thermal treatment techniques. It is found that the interwoven ultrathin Co₃O₄ nanopetals evenly grow on the nanoporous CuO network (Co₃O₄@NP-CuO). The three-dimensional (3D) hierarchical porous structure for the catalyst provides more surface area to act as active sites and facilitates the absorption of visible light in the photodegradation reaction. Compared with the commercial CuO and Co₃O₄ powders, the newly designed Co₃O₄@NP-CuO composite exhibits superior photodegradation performance for RhB. The enhanced performance is mainly due to the construction of heterojunction of Co₃O₄/CuO, greatly promoting the efficient carrier separation for photocatalysis. Furthermore, the possible photocatalytic mechanism is analyzed in detail. This work provides a promising strategy for the fabrication of a new controllable heterojunction to improve photocatalytic activity.

Nano-remediation technologies for the sustainable mitigation of persistent organic pollutants

The absence of novel and efficient methods for the elimination of persistent organic pollutants (POPs) from the environment is a serious concern in the society. The pollutants release into the atmosphere by means of industrialization and urbanization is a massive global hazard. Although, the eco-toxicity associated with nanotechnology is still being debated, nano-remediation is a potentially developing tool for dealing with contamination of the environment, particularly POPs. Nano-remediation is a novel strategy to the safe and long-term removal of POPs. This detailed review article presents an important perspective on latest innovations and future views of nano-remediation methods used for environmental decontamination, like nano-photocatalysis and nanosensing. Different kinds of nanomaterials including nanoscale zero-valent iron (nZVI), carbon nanotubes (CNTs), magnetic and metallic nanoparticles, silica (SiO₂) nanoparticles, graphene oxide, covalent organic frameworks (COFs), and metal organic frameworks (MOFs) have been summarized for the mitigation of POPs. Furthermore, the long-term viability of nano-remediation strategies for dealing with legacy contamination was considered, with a particular emphasis on environmental and health implications. The assessment goes on to discuss the environmental consequences of nanotechnology and offers consensual recommendations on how to employ nanotechnology for a greater present and a more prosperous future.

Degradation of Organic Dyes Using the Ionizing Irradiation Process in the Presence of the CN/CD3/Fe6 Composite: Mechanistic Studies

Organic dyes are ubiquitous pollutants in various aquatic environments as they are produced in abundance and used widely. In the present work, the degradation and mineralization of various organic dyes such as methylene blue (MB), methyl orange (MO), and rhodamine B (RhB), following the electron beam irradiation method in the presence of a graphitic carbon nitride/carbon nanodots/Fe(II) (CN/CD₃/Fe₆) composite, were studied. The removal efficiency of MB reached 81.7% under conditions of electron beam irradiation (EBI) when the total irradiation dose was 5 kGy. This increased to 91.2% in the presence of the CN/CD₃/Fe₆ composite. The mineralization efficiency increased from 30.1 to 47.3% when the composite was added, and the total irradiation dose was 20 kGy. The removal efficiency of organic dyes was not significantly affected in the pH range of 3-11. Results from cyclic experiments conducted using MB degradation indicated that the CN/CD₃/Fe₆ composite exhibited good stability and reusability even after five irradiation cycles. Results from scavenging experiments revealed that ^•OH was the predominant reactive species during the MB degradation process. Intermediates produced in the synergistic system (EBI&CN/CD₃/Fe₆ system) consisting of the CN/CD₃/Fe₆ composite and EBI were detected using the liquid chromatography-mass spectrometry (LC-MS) technique. Based on the results, the possible degradation mechanism and pathways for MB were proposed.

Using biobeds for the treatment of fungicide-contaminated effluents from various agro-food processing industries: Microbiome responses and mobile genetic element dynamics

Agro-food processing industries generate large amounts of pesticide-contaminated effluents that pose a significant environmental threat if managed improperly. Biopurification systems like biobeds could be utilized for the depuration of these effluents although direct evidence for their efficiency are still lacking. We employed a column leaching experiment with pilot biobeds to (i) assess the depuration potential of biobeds against fungicide-contaminated effluents from seed-producing (carboxin, metalaxyl-M, fluxapyroxad), bulb-handling (thiabendazole, fludioxonil and chlorothalonil) and fruit-packaging (fludioxonil, imazalil) industries, (ii) to monitor microbial succession via amplicon sequencing and (iii) to determine the presence and dynamics of mobile genetic elements like intl1, IS1071, IncP-1 and IncP-1ε often associated with the transposition of pesticide-degrading genes. Biobeds could effectively retain (adsorbed but extractable with organic solvents) and dissipate (degraded and/or not extractable with organic solvents) the fungicides that were contained in the agro-industrial effluents with 93.1-99.98% removal efficiency in all cases. Lipophilic substances like fluxapyroxad were mostly retained in the biobed while more polar substances like metalaxyl-M and carboxin were mostly dissipated or showed higher leaching potential like metalaxyl-M. Biobeds supported a bacterial and fungal community that was not affected by fungicide application but showed clear temporal patterns in the different biobed horizons. This was most probably driven by the establishment of microaerophilic conditions upon water saturation of biobeds, as supported by the significant increase in the abundance of facultative or strict anaerobes like Chloroflexi/Anaerolinae, Acidibacter and Myxococcota. Wastewater application did not affect the dynamics of mobile genetic elements in biobeds whose abundance (intl1, IS1071, IncP-1ε) showed significant increases with time. Our findings suggest that biobeds could effectively decontaminate fungicide-contaminated effluents produced by agro-food industries and support a rather resilient microbial community.

Prospecting carbon-based nanomaterials for the treatment and degradation of endocrine-disrupting pollutants

The presence of endocrine-disrupting chemicals (EDCs) in water resources has significant negative implications for the environment. Traditional technologies implemented for water treatment are not completely efficient for removing EDCs from water. Therefore, research on sustainable remediation has been mainly directed to novel decontamination approaches including nano-remediation. This emerging technology employs engineered nanomaterials to clean up the environment quickly, efficiently, and sustainably. Thus, nanomaterials have contributed to a wide variety of remediation techniques like adsorption, filtration, coagulation/flocculation, and so on. Among the vast diversity of decontamination technologies catalytic advanced oxidation processes (AOPs) outstand as simple, clean, and efficient alternatives. A vast diversity of catalysts has been developed demonstrating high efficiencies; however, the search for novel catalysts with enhanced performances continues. In this regard, nanomaterials used as nanocatalysts are exhibiting enhanced performances on AOPs due to their special nanostructures and larger specific surface areas. Therefore, in this review we summarize, compare, and discuss the recent advances on nanocatalysts, catalysts doped with metal-based nanomaterials, and catalysts doped with carbon-based nanomaterials on the degradation of EDCs. Finally, further research opportunities are identified and discussed to achieve the real application of nanomaterials to efficiently degrade EDCs from water resources.

Effects of nitrogen/bismuth-doping on the photocatalyst composite of carbon dots/titanium dioxide nanoparticles (CDs/TNP) for enhanced visible light-driven removal of diclofenac

The present work demonstrates the coupling of titanium dioxide, TiO₂ nanoparticles (TNP) with N-doped, Bi-doped, and N-Bi co-doped rice husk-derived carbon dots (CDs) via a facile dispersion method, forming respective photocatalyst composites of CDs/TNP, N-CDs/TNP, Bi-CDs/TNP and N-Bi-CDs/TNP. Characterization analyzes verified the successful incorporation of respective CDs samples into TNP, forming photocatalyst composite with narrowed band gap and quenched photoluminescence intensity. Photocatalytic activity of TNP and the respective composites was investigated for photodegradation of diclofenac (DCF) under both simulated sunlight and natural sunlight irradiation. The as-prepared N-Bi-CDs/TNP composite showed the best photocatalytic performance among all composites, able to completely degrade 5 ppm of DCF within 60 min and 180 min under both types of visible light irradiation, respectively. The N-Bi-CDs/TNP composite also showed a TOC removal efficiency up to 87.63%. N-Bi-CDs, worked as photosensitizer and electron reservoir, contributed to the outstanding photocatalytic activity of N-Bi-CDs/TNP, whereby the recombination was prolonged and light absorption was shifted towards the visible light region. Furthermore, the composite of N-Bi-CDs/TNP also demonstrated good stability and reusability over repeated degradation cycles. The photodegradation of DCF resulted into several intermediates, which were identified from LC-MS analysis. The present work could provide an insight on the application of heteroatoms doped and co-doped carbon dots in semiconductor oxide as high performance photocatalysts.

Analytical and regulatory considerations to mitigate highly hazardous toxins from environmental matrices

The ubiquitous occurrence, toxicological influence, and bioaccumulation of toxic entities, e.g., pesticides and toxic elements in the environment, biota, and humans, directly or indirectly, are posing severe social, ecological, and human health concerns. Much attention has been given to the rising bioaccumulation of toxins and their adverse impact on various environmental matrices. For example, the inappropriate and exacerbated use of xenobiotics and related hazardous substances have caused the deterioration of the agricultural environment, e.g., fertile soils where plants are grown. Moreover, the harmful toxins have negatively impacted human health through the trophic chains. However, the analytical and regulatory considerations to effectively monitor and mitigate any or many pesticides and toxic elements from environmental matrices are still lacking in the existing literature. For decades, the scientific community has overseen the consequences caused by pollutants, however, the improvement of analytical detection methods and regulatory considerations are not yet fully covered. This review covers the notable literature gap by stressing the development and deployment of robust analytical and regulatory considerations for an efficient abatement of hazardous substances. Following detailed information on occurrence, toxicological influence, and bioaccumulation of pesticides and toxic elements, the most relevant analytical detection tools and regulatory measures are given herein, with suitable examples, to mitigate or reduce the damage caused by these pollutants.

Covalent organic frameworks-based smart materials for mitigation of pharmaceutical pollutants from aqueous solution

Covalent organic frameworks (COFs) are an emergent group of crystalline porous materials that have gained incredible interest in recent years. With foreseeable controllable functionalities and structural configurations, the constructions and catalytic properties of these organic polymeric materials can be controlled to fabricate targeted materials. The specified monomer linkers and pre-designed architecture of COFs facilitate the post-synthetic modifications for introducing novel functions and useful properties. By virtue of inherent porosity, robust framework, well-ordered geometry, functionality, higher stability, and amenability to functionalization, COFs and COFs-based composites are regarded as prospective nanomaterials for environmental clean-up and remediation. This report spotlights the state-of-the-art advances and progress in COFs-based materials to efficiently mitigate pharmaceutical-based environmental pollutants from aqueous solutions. Synthesis approaches, structure, functionalization, and sustainability aspects of COFs are discussed. Moreover, the adsorptive and photocatalytic potential of COFs and their derived nanocomposites for removal and degradation of pharmaceuticals are thoroughly vetted. In addition to deciphering adsorption mechanism/isotherms, the stability, regeneratability and reproducibility are also delineated. Lastly, the outcomes are summed up, and new directions are proposed to widen the promise of COF-based smart materials in diverse fields.