Pd@Na-CMC/g-C3N4: A nanostructured catalyst system based on sodium carboxymethyl cellulose/graphitic carbon nitride hydrogel beads and its performance in the treatment of organic and inorganic pollutants in water

The chemical reduction of organic or inorganic water contaminants is very important for both human health and pollution control. However, challenges still persist in preparing catalysts for chemical reduction, and there is a need for the development of inexpensive, easily synthesized, and effective catalyst systems. In this study, we have synthesized a new palladium nanocatalyst supported on the composite hydrogel beads composed of sodium carboxymethyl cellulose (Na-CMC) and graphitic carbon nitride (g-C3N4). The Pd@Na-CMC/g-C3N4 composite was fully characterized using FE-SEM, XRD, BET, EDS, TEM, and EDS mapping analysis, confirming its successful preparation at the nano-scale. Pd@Na-CMC/g-C3N4 was utilized to reduce various nitroaromatics such as 4-nitrophenol (4-NP), 2-nitrophenol (2-NA), 4-nitroaniline (4-NA), 4-nitro-o-phenylenediamine (4-NPDA), and organic dyes including methylene blue (MB), methyl orange (MO), Rhodamine B (RhB), as well as potassium hexacyanoferrate(III) (K3[Fe(CN)6]), which is the inorganic contaminant. While Pd@Na-CMC/g-C3N4 completely reduced nitroaromatics within 65-120 s at 1 × 10-4 M concentration, organic dyes within 0-60 s at 1 × 10-5 M concentration, and K3[Fe(CN)6] within 90 s at 0.002 M concentration in water at room temperature. Rate constant values (kapp) of 4-NP, 2-NA, 4-NA, 4-NPDA, MO, RhB, and K3[Fe(CN)6] were calculated to be 0.0085 s-1, 0.012 s-1, 0.016 s-1, 0.01 s-1, 0.013 s-1, 0.021 s-1, and 0.015 s-1, respectively. Additionally, the Pd@Na-CMC/g-C3N4 displayed high stability and even after four consecutive runs, it was able to reduce 4-NP and MO without any significant loss in its performance.

Enhanced photocatalytic activity of magnetically recyclable spherical Fe3O4/Cu2O S-scheme heterojunction

In this study, magnetically recyclable spherical Fe3O4/Cu2O particles comprising S-scheme heterojunctions were prepared by a simple hydrothermal approach using n-type semiconductor Fe3O4 as precursor and p-type semiconductor Cu2O. A Fenton-like system was thus constructed via the addition to Fe3O4/Cu2O of hydrogen peroxide. A rhodamine B (RhB) solution was used to simulate polluted wastewater, and photocatalytic RhB removal experiments were conducted under visible light irradiation. Powder X-ray diffractometry, vibrating-sample magnetometry, nitrogen adsorption-desorption, transmission electron microscopy, and X-ray photoelectron spectroscopy experiments were conducted to characterise Fe3O4 and Fe3O4/Cu2O composite. The band gap of Fe3O4/Cu2O was 1.76 eV, narrower than that of Fe3O4 (2.14 eV). The effects of the pH, sample dosage, hydrogen peroxide concentration, and RhB initial concentration on RhB removal were investigated. According to evidence, under the optimum reaction conditions, the RhB removal rate was 99.4%. The Fe3O4/Cu2O composite exhibited good photocatalytic efficacy even after four cycles of testing. Based on the results of free radical capture experiments, hydroxyl radicals and holes cooperated as main reactive species in the photocatalytic system. The Fe3O4/Cu2O photocatalyst can be easily removed based on magnetism, and it has been proven to be very effective for the degradation of RhB under both UV and visible light irradiation.

Hematite (α-Fe2O3) with Oxygen Defects: The Effect of Heating Rate for Photocatalytic Performance

Hematite (α-Fe2O3) emerges as an enticing material for visible-light-driven photocatalysis owing to its remarkable stability, low toxicity, and abundance. However, its inherent shortcomings, such as a short hole diffusion length and high recombination rate, hinder its practical application. Recently, oxygen vacancies (Vo) within hematite have been demonstrated to modulate its photocatalytic attributes. The effects of Vo can be broadly categorized into two opposing aspects: (1) acting as electron donors, enhancing carrier conductivity, and improving photocatalytic performance and (2) acting as surface carrier traps, accelerating excited carrier recombination, and deteriorating performance. Critically, the generation rate, distribution, role, and behavior of Vo significantly differ for synthesis methods due to differences in formation mechanisms and oxygen diffusion. This complexity hampers simplified discussions of Vo, necessitating careful investigation and nuanced discussion tailored to the specific method and conditions employed. Among various approaches, hydrothermal synthesis offers a simple and cost-effective route. Here, we demonstrate a hydrothermal synthesis method for Vo introduction to hematite using a carbon source, where variations in the heating rate have not been previously explored in terms of their influence on Vo generation. The analyses revealed that the concentration of Vo was maximized at a heating rate of 16 °C/min, indicative of a high density of surface defects. With regard to photocatalytic performance, elevated heating rates (16 °C/min) fostered the formation of Vo primarily on the hematite surface. The photocatalytic activity was 7.1 times greater than that of the sample prepared at a low heating rate (2 °C/min). These findings highlight the crucial role of surface defects, as opposed to bulk defects, in promoting hematite photocatalysis. Furthermore, the facile control over Vo concentration achievable via manipulating the heating rate underscores the promising potential of this approach for optimizing hematite photocatalysts.

A review of biosensor for environmental monitoring: principle, application, and corresponding achievement of sustainable development goals

Human health/socioeconomic development is closely correlated to environmental pollution, highlighting the need to monitor contaminants in the real environment with reliable devices such as biosensors. Recently, variety of biosensors gained high attention and employed as in-situ application, in real-time, and cost-effective analytical tools for healthy environment. For continuous environmental monitoring, it is necessary for portable, cost-effective, quick, and flexible biosensing devices. These benefits of the biosensor strategy are related to the Sustainable Development Goals (SDGs) established by the United Nations (UN), especially with reference to clean water and sources of energy. However, the relationship between SDGs and biosensor application for environmental monitoring is not well understood. In addition, some limitations and challenges might hinder the biosensor application on environmental monitoring. Herein, we reviewed the different types of biosensors, principle and applications, and their correlation with SDG 6, 12, 13, 14, and 15 as a reference for related authorities and administrators to consider. In this review, biosensors for different pollutants such as heavy metals and organics were documented. The present study highlights the application of biosensor for achieving SDGs. Current advantages and future research aspects are summarized in this paper.Abbreviations: ATP: Adenosine triphosphate; BOD: Biological oxygen demand; COD: Chemical oxygen demand; Cu-TCPP: Cu-porphyrin; DNA: Deoxyribonucleic acid; EDCs: Endocrine disrupting chemicals; EPA: U.S. Environmental Protection Agency; Fc-HPNs: Ferrocene (Fc)-based hollow polymeric nanospheres; Fe₃O₄@3D-GO: Fe₃O₄@three-dimensional graphene oxide; GC: Gas chromatography; GCE: Glassy carbon electrode; GFP: Green fluorescent protein; GHGs: Greenhouse gases; HPLC: High performance liquid chromatography; ICP-MS: Inductively coupled plasma mass spectrometry; ITO: Indium tin oxide; LAS: Linear alkylbenzene sulfonate; LIG: Laser-induced graphene; LOD: Limit of detection; ME: Magnetoelastic; MFC: Microbial fuel cell; MIP: Molecular imprinting polymers; MWCNT: Multi-walled carbon nanotube; MXC: Microbial electrochemical cell-based; NA: Nucleic acid; OBP: Odorant binding protein; OPs: Organophosphorus; PAHs: Polycyclic aromatic hydrocarbons; PBBs: Polybrominated biphenyls; PBDEs: Polybrominated diphenyl ethers; PCBs: Polychlorinated biphenyls; PGE: Polycrystalline gold electrode; photoMFC: photosynthetic MFC; POPs: Persistent organic pollutants; rGO: Reduced graphene oxide; RNA: Ribonucleic acid; SDGs: Sustainable Development Goals; SERS: Surface enhancement Raman spectrum; SPGE: Screen-printed gold electrode; SPR: Surface plasmon resonance; SWCNTs: single-walled carbon nanotubes; TCPP: Tetrakis (4-carboxyphenyl) porphyrin; TIRF: Total internal reflection fluorescence; TIRF: Total internal reflection fluorescence; TOL: Toluene-catabolic; TPHs: Total petroleum hydrocarbons; UN: United Nations; VOCs: Volatile organic compounds.

Heterogeneous photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) with dual Z-Scheme heterojunction for degradation of tetracycline

A novel photo-Fenton catalyst α-Fe2O3@g-C3N4@NH2-MIL-101(Fe) (FGN) with dual Z-scheme heterojunction was successfully prepared by hydrothermal method to degrade tetracycline (TC). The preparation conditions were optimized by orthogonal test, and the successful synthesis was confirmed by characterization analyses. The prepared FGN showed better light absorption performance, higher photoelectrons-holes separation efficiency, lower photoelectrons transfer resistance, and higher specific surface area and pore capacity compared with α-Fe2O3@g-C3N4 and α-Fe2O3. The effects of experimental conditions on the catalytic degradation of TC were investigated. The degradation rate of 10 mg/L TC could reach 98.33% within 2 h when the dosage of FGN was 200 mg/L, and the degradation rate could remain 92.27% after 5 times of reuse. Furthermore, the XRD spectra and XPS spectra of FGN before and after reuse were compared to explore the structural stability and catalytic active sites of FGN, respectively. According to the identification of oxidation intermediates, three degradation pathways of TC were proposed. Through H2O2 consumption experiment, radical-scavenging experiments, EPR results, the mechanism of the dual Z-scheme heterojunction was proved. The improved performance of FGN was attributed to the dual Z-Scheme heterojunction effectively promoting the separation of photogenerated electrons from the holes and accelerating the electrons transfer, and the increase of the specific surface area.

An overview on ZnO-based sonophotocatalytic mitigation of aqueous phase pollutants

Over the past several decades, the increase in industrialization provoked the discharge of harmful pollutants into the environment, affecting human beings and ecosystems. ZnO-based photocatalysts seem to be the most promising photocatalysts for treating harmful pollutants. However, fast charge carrier recombination, photo corrosion, and long reaction time are the significant factors that reduce the photoactivity of ZnO-based photocatalysts. In order to enhance the photoactivity of such photocatalysts, a combined process i.e., sonocatalysis + photocatalysis = sonophotocatalysis was used. Sonophotocatalysis is one of several different AOP methods that have recently drawn considerable interest, as it produces high reactive oxygen species (ROS) which helps in the oxidation of pollutants by acoustic cavitation. This combined technique enhanced the overall efficiency of the individual method by overcoming its limiting factors. The current review aims to present the theoretical and fundamental aspects of sonocatalysis and photocatalysis along with a detailed discussion on the benefits that can be obtained by the combined process i.e., US + UV (sonophotocatalysis). Also, we have provided a comparison of the excellent performance of ZnO to that of the other metal oxides. The purpose of this study is to discuss the literature concerning the potential applications of ZnO-based sonophotocatalysts for the degradation of pollutants i.e., dyes, antibiotics, pesticides, phenols, etc. That are carried out for future developments. The role of the produced ROS under light and ultrasound stimulation and the degradation mechanisms that are based on published literature are also discussed. In the end, future perspectives are suggested, that are helpful in the development of the sonophotocatalysis process for the remediation of wastewater containing various pollutants.

In-situ development of boron doped g-C3N4 supported SBA-15 nanocomposites for photocatalytic degradation of tetracycline

In this study, versatile boron-doped graphitic carbon nitride (gCN) incorporated mesoporous SBA-15 (BGS) composite materials were prepared by thermal polycondensation method using boric acid & melamine as a B-gCN source material and SBA-15 as mesoporous support. The prepared BGS composites are utilized sustainably using solar light as the energy source for the continuous flow of photodegradation of tetracycline (TC) antibiotics. This work highlights that the photocatalysts preparation was carried out with an eco-friendly strategy, solvent-free and without additional reagents. To alter the amount of boron quantity (0.124 g, 0.248 g, and 0.49 g) have to prepare three different composites using a similar procedure, the obtained composites viz., BGS-1, BGS-2 and BGS-3, respectively. The physicochemical property of the prepared composites was investigated by X-ray diffractometry, Fourier-transform infrared spectroscopy, Raman, Diffraction reflectance spectra, Photoluminescence, Brunauer-Emmett-Teller and transmission electron microscopy (TEM). The results shows that 0.24 g boron- loaded BGS composites degrade TC up to 93.74%, which is much higher than the rest of the catalyst. The addition of mesoporous SBA-15 incresed the specific surface area of the g-CN, and heteroatom of boron increased the interplanar stracking distance of g-CN, enlarged the optical absorption range, reducing the energy bandgap and enhanced the photocatalytic activity of TC. Additionally, the stability and recycling efficiency of the representative photocatalysts viz., BGS-2 was observed to be good even at the fifth cycle. The photocatalytic process using the BGS composites demonstrated to be capable candidate for the removal of tetracycline biowaste from aquesous media.

Boosted photocatalytic performance of OVs-rich BiVO4 hollow microsphere self-assembled with the assistance of SDBS

In this study, monoclinic phase bismuth vanadate (BiOV₄) photocatalyst with unique hollow microsphere morphology was successfully prepared by a hydrothermal method in the existence of sodium dodecyl benzene sulfonate (SDBS). The prepared photocatalysts were characterized by X-ray diffraction (XRD), scanning electron (SEM) and X-ray photoelectron spectrometer (XPS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). Experimental results show that SDBS definitely changes the microstructure of BiVO₄, which is allocated to the template role of SDBS in the preparation process. Moreover, the hydrothermal treatment time is also of crucial importance in affecting the structure and morphology of the photocatalysts, and the optimal hydrothermal treatment time for the formation of hollow microsphere is 24 h. Furthermore, the feasible growth mechanism for hollow microsphere was elaborated. Enriched oxygen vacancies (OVs) are introduced into BiOV₄ prepared with SDBS, largely elevating the separation efficiency of photo-generated charges. Under visible light irradiation, the photocatalytic activities of BiOV₄ for destruction of rhodamine (RhB) were evaluated. The photocatalytic degradation rate constant of RhB on the 3SBVO is 2.23 times of that on the blank BiOV₄ as the mass ratio of SDBS/BiOV₄ is 3 %. Photocatalytic degradation mechanism of BiVO₄ toward detoxification of organic pollutants was presented.

A Z-scheme BiYO3/g-C3N4 heterojunction photocatalyst for the degradation of organic pollutants under visible light irradiation

Photocatalysis is one of the fascinating fields for the wastewater treatment. In this regard, the present study deals with an effective visible light active BiYO₃/g-C₃N₄ heterojunction nanocomposite photocatalyst with various ratios of BiYO₃ and g-C₃N₄ (1:3, 1:1 and 3:1), synthesised by a wet chemical approach. The as-synthesised nanocomposite photocatalysts were investigated via different physicochemical approaches like Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electrons microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and photoelectrochemical studies to characterise the crystal structure, morphology, optical absorption characteristics and photoelectrochemical properties. The photocatalytic degradation ability of the prepared photocatalytic samples was also analysed through the degradation of RhB in the presence of visible light irradiation. Of all the synthesised photocatalysts, the optimised CB-1 composite showed a significant photocatalytic efficiency (88.7%), with excellent stability and recyclability after three cycles. O₂^•- and ^•OH radicals were found to act a major role in the RhB degradation using optimised CB-1 composite, and it possessed ~ 1 times greater photocurrent intensity than the pristine g-C₃N₄ and BiYO₃. In the present work, a direct Z-scheme heterojunction BiYO₃/g-C₃N₄ with a considerably improved photocatalytic performance is reported.

Construction of direct FeMoO4/g-C3N4-2D/2D Z-scheme heterojunction with enhanced photocatalytic treatment of textile wastewater to eliminate the toxic effect in marine environment

A novel FeMoO₄/g-C₃N₄-2D/2D Z-scheme heterojunction photocatalyst was prepared via wet chemical method. The observed structural morphology of FeMoO₄/g-C₃N₄ reveals the 2D-iron molybdate (FeMoO₄) nanoplates compiled with the 2D-graphitic carbon nitride (g-C₃N₄) nanosheets like structure. The photocatalytic activity of the g-C₃N₄, FeMoO₄, and FeMoO₄/g-C₃N₄ composites were studied via the degradation of Rhodamine B (RhB) as targeted textile dye under visible light irradiation (VLI). The optimal FeMoO₄/g-C₃N₄ (1:3 ratio of g-C₃N₄ and FeMoO₄) composite show an enhanced degradation performance with rate constant value of 0.02226 min^-1 and good stability even after three cycles. Thus, the h+ and O₂^•－are the key radicals in the degradation of RhB under VLI. It is proposed that the FeMoO₄/g-C₃N₄ Z-scheme heterojunction effectively enhances the transfer and separation ability of e^-/h⁺ pairs, by the way increasing the photocatalytic efficiency towards the RhB degradation. Thus, the newly constructed Z-scheme FeMoO₄/g-C₃N₄ heterojunction photocatalyst is a promising material for the remediation of wastewater relevant to elimination of toxic effect in marine environment.

Photodegradation of ciprofloxacin antibiotic in water by using ZnO-doped g-C3N4 photocatalyst

Ciprofloxacin antibiotic (CIP) is one of the antibiotics with the highest rate of antibiotic resistance, if used and managed improperly, can have a negative impact on the ecosystem. In this research, ZnO modified g-C₃N₄ photocatalyst was prepared and applied for the decomposition of CIP antibiotic compounds in water. The removal performance of CIP by using ZnO/g-C₃N₄ reached 93.8% under pH 8.0 and an increasing amount of catalyst could improve the degradation performance of the pollutant. The modified ZnO/g-C₃N₄ completely oxidized CIP at a low concentration of 1 mg L^-1 and the CIP removal efficiency slightly decreases (around 13%) at a high level of pollutant (20 mg L^-1). The degradation rate of CIP by doped sample ZnO/g-C₃N₄ was 4.9 times faster than that of undoped g-C₃N₄. The doped catalyst ZnO/g-C₃N₄ also displayed high reusability for decomposition of CIP with 89.8% efficiency remaining after 3 cycles. The radical species including ·OH, ·O₂^- and h⁺ are important in the CIP degradation process. In addition, the proposed mechanism for CIP degradation by visible light-assisted ZnO/g-C₃N₄ was claimed.

Architecture of visible-light induced Z-scheme MoS2/g-C3N4/ZnO ternary photocatalysts for malachite green dye degradation

The synthesis of bilayer heterojunctions has received considerable attention recently. Fabrication of novel bilayer composites is of significant interest to improve their photocatalytic efficiency. In this study, molybdenum disulfide (MoS₂), a layered dichalcogenide material exhibiting unique properties, in combination with graphitic carbon nitride (g-C₃N₄), a carbon-based layered material, was fabricated with small amounts of zinc oxide (ZnO). Three composites, MoS₂/g-C₃N₄, MoS₂/ZnO, and MoS₂/g-C₃N₄/ZnO were prepared via a simple exfoliation method and characterized by various physicochemical methods. The Z-scheme charge transfer mechanism in the prepared ternary composite improves efficiency by inhibiting the recombination rate of electron-hole pairs. It has shown excellent performance in degrading a major water contaminant, malachite green (MG) dye, under visible light irradiation.

Graphitic carbon nitride (g-C3N4)-based photocatalytic materials for hydrogen evolution

The semiconductors, such as TiO₂, CdS, ZnO, BiVO₄, graphene, produce good applications in photocatalytic water splitting for hydrogen production, and great progress have been made in the synthesis and modification of the materials. As a two-dimensional layered structure material, graphitic carbon nitride (g-C₃N₄), with the unique properties of high thermostability and chemical inertness, excellent semiconductive ability, affords good potential in photocatalytic hydrogen evolution. However, the related low efficiency of g-C₃N₄ with fast recombination rate of photogenerated charge carriers, limited visible-light absorption, and low surface area of prepared bulk g-C₃N₄, has called out the challenge issues to synthesize and modify novel g-C₃N₄-block photocatalyst. In this review, we have summarized several strategies to improve the photocatalytic performance of pristine g-C₃N₄ such as pH, morphology control, doping with metal or non-metal elements, metal deposition, constructing a heterojunction or homojunction, dye-sensitization, and so forth. The performances for photocatalytic hydrogen evolution and possible development of g-C₃N₄ materials are shared with the researchers interested in the relevant fields hereinto.

Magnetically Recoverable Biomass-Derived Carbon-Aerogel Supported ZnO (ZnO/MNC) Composites for the Photodegradation of Methylene Blue

Hydrothermally assisted magnetic ZnO/Carbon nanocomposites were prepared using the selective biowaste of pomelo orange. Initially, the carbon aerogel (CA) was prepared hydrothermally followed by a freeze-drying method. Furthermore, the iron oxide nanoparticles were deposited onto the surface of carbon using the co-precipitation method and we obtained magnetic carbon nanocomposite, i.e., Fe3O4/C (MNC). Moreover, the ZnO photocatalysts were incorporated onto the surface of MNC composites using a hydrothermal process, and we obtained ZnO/MNC composites. The ZnO/MNC (55%), ZnO/MNC (65%) and ZnO/MNC (75%) composites were prepared by a similar experimental method in order to change the weight ratio of ZnO NPs. Using a similar synthetic procedure, the standard ZnO and Fe3O4 nanoparticles were prepared without the addition of CA. The experimental results were derived from several analytical techniques, such as: X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman and diffuse reflectance spectroscopy (DRS-UV). The synthesized carbon, ZnO, Fe3O4, ZnO/MNC (55%), ZnO/MNC (65%) and ZnO/MNC (75%) composites were examined through the photocatalytic degradation of methylene blue (MB) under visible-light irradiation (VLI). The obtained results revealed that the composites were more active than carbon, ZnO and Fe3O4. In particular, the ZnO/MNC (75%) composites showed more activity than the rest of the composites. Furthermore, the recycling abilities of the prepared ZnO/MNC (75%) composites were examined through the degradation of MB under identical conditions and the activity remained constant up to the fifth cycle. The synthetic procedure and practical applications proposed here can be used in chemical industries, biomedical fields and energy applications.

Robust visible light active CoNiO2-BiFeO3-NiS ternary nanocomposite for photo-fenton degradation of rhodamine B and methyl orange: Kinetics, degradation pathway and toxicity assessment

Sustainable wastewater treatment is crucial to remediate the water pollutants through the development of highly efficient, low-cost and separation free photocatalyst. The aim of this study is to construct a novel CoNiO₂-BiFeO₃-NiS ternary nanocomposite (NCs) for the efficient degradation of organic pollutants by utilising visible light. The NCs was characterized by various physiochemical techniques, including HR-TEM, SEM, XPS, FT-IR, ESR, EIS, PL, UV-visible DRS, and N₂ adsorption and desorption analysis. The photocatalyst exhibits extraordinary degradation efficiency towards MO (99.8%) and RhB (97.8%). The intermediates were determined using GC-MS analysis and the degradation pathway was elucidated. The complete mineralization was further confirmed by TOC analysis. The CoNiO₂-BiFeO₃-NiS ternary NCs have shown excellent photostability, structural stability and reusability even after six cycles and it is confirmed by XRD and XPS analysis. The kinetic study reveals that the photodegradation of the dyes follows first order reaction. The influence of different pH, dye concentrations and NCs dosages were investigated. The intermediate toxicity was predicted by computational stimulation using ECOSAR software. The NCs shows promising potential for ecological safety which demonstrates its practical application in the treatment of waste water pollutants in large scale.

Metal-Doped Graphitic Carbon Nitride Nanomaterials for Photocatalytic Environmental Applications—A Review

In the current world situation, population and industrial growth have become major problems for energy and environmental concerns. Extremely noxious pollutants such as heavy metal ions, dyes, antibiotics, phenols, and pesticides in water are the main causes behind deprived water quality leading to inadequate access to clean water. In this connection, graphite carbon nitride (GCN or g-C3N4) a nonmetallic polymeric material has been utilized extensively as a visible-light-responsive photocatalyst for a variety of environmental applications. This review focuses on recent developments in the design and photocatalytic applications of metal-doped GCN-based nanomaterials in CO2 photoreduction, water splitting toward hydrogen production, bacterial disinfection, and organic pollutant degradation. Additionally, this review discusses various methods of using GCN-based materials to optimize dye sensitization, metal deposition, ion doping, and their environmental applications.

Microwave assisted hydrothermally synthesized cobalt doped zinc ferrites nanoparticles for the degradation of organic dyes and antimicrobial applications

A novel photocatalyst based cobalt doped zinc ferrites nanoparticles (Co-ZnFe₂O₄ NPs) was prepared to actively concentrate degradation of organic dyes in water. The aim this study is to investigate the effect of substitution of Co²⁺ for Zn²⁺ in zinc ferrites nanoparticles and is characterized with UV-visible spectroscopy, XRD, TEM, SEM, Photoluminescence and Vibrating sample magnetometer technique. When the calcinations temperature increases from 150 °C to 450 °C the amorphous ferrites begins to vanish and the characteristic reflections of cubic spinal Co-ZnFe₂O₄ phase are only observed at 450 °C. The band gap energy (E_g) of sample calcined at 250 °C is calculated at 5.2 eV and that of 450 °C is 4.5 eV. The observed value of band gap energy decreased with increasing calcinations temperature in the samples. The increase in PL peak intensity is due to collective emissions and light-scattering. The doping material, cobalt substitution at spinel zinc ferrites surface, and hence gradually decrease the amorphous effect, increase the saturation magnetization and decrease the coercivity while increasing the temperature. The compounds calcined at 250 °C and 450 °C were investigated for their in vitro antimicrobial activity against Staphylococcus aureus. A sample with 450 °C calcination temperature leads to higher efficiencies in the inhibition of growth of bacteria and degradation of organic dyes. Hence, this study provides a novel photocatalyst of Co-ZnFe₂O₄ NPs in the tile to degrade and analyze the environmentally ignored organic compounds.

Diclofenac removal from the wastewater using activated sludge and analysis of multidrug resistant bacteria from the sludge

Diclofenac is an anti-inflammatory drug and has been frequently detected from the wastewater. In the present study, factors affecting diclofenac adsorption on sewage sludge was evaluated. At 1 mg/L initial diclofenac concentration, more than 80% diclofenac removal was achieved. Adsorption increased at higher concentration (100 mg/L concentration) and more than 99% diclofenac was adsorbed from the wastewater. Significant removal of diclofenac was observed after 5 min contact time. The adsorption efficacy was more than 98% after 50 and 60 min. Pseudo-first and second order kinetics revealed reasonable regression value (0.9) indicated that the model is best fitted. Diclofenac adsorption was extremely high at acidic pHs than alkaline range. The sludge samples showed the presence of multi drug resistant bacteria. Vancomycin-resistant enterococcus stains were 27%, Methicillin-resistant Staphylococcus aureus positive strains were 16.5% and Extended-spectrum betal-lactamase-harbouring Enterobacteriacea were 65.4% in the sludge. The drug resistance Enterobacteriaceae revealed 14 Klebsiella pneumonia strains, 11 strains from E. coli and two from the genus Enterobacter. To conclude, the activated sludge could be effectively utilized for the removal of diclofenac from wastewater.

Complete photocatalytic degradation of tetracycline by carbon doped TiO2 supported with stable metal nitrate hydroxide

Visible light-driven carbon-doped TiO₂ supported with metal nitrate hydroxide (CT-Ni/Co/Cu) nanocomposites were prepared and characterized by various studies. It is fascinating to note that particle size of TiO₂ was substantially reduced from 5 μm to 50 nm after doping of carbon which was confirmed by FESEM. Moreover, the incorporation of stable metal (Cu) nitrate hydroxide further enhanced the visible light absorption up to 800 nm as evident by UV-DRS. The carbon doping and copper nitrate formation are validated by the Ti-O-C and N-O bonds using XPS and FTIR spectra. The photocatalytic activity of as-prepared photocatalyst was tested for the tetracycline degradation (TC, 10 mg/mL) under light irradiation. Significantly, 3 wt% carbon-doped TiO₂ (31CT) with Cu (II) hydroxide nitrate nanocomposite photocatalyst exhibited an excellent photocatalytic activity (97%, within 1 h), and the corresponding reaction rate was around 2 times higher than bare TiO₂. The excellent photocatalytic activity of 31CT-Cu nanocomposite was due to enhanced adsorbent of TC via carbon doping, visible light absorption, improved photo-generated carrier separation and migration by metal nitrate hydroxide as a support. This work may promote the development of a new carbon-doped TiO₂ supported with highly stable metal nitrate hydroxide nanocomposite by facile method and used as an efficient photocatalyst for photodegradation of environmental pollutants.

Chitosan magnetic graphene grafted polyaniline doped with cobalt oxide for removal of Arsenic(V) from water

The present study reports the successful functionalization/magnetization of bio-polymer to produce chitosan-magnetic graphene oxide grafted polyaniline doped with cobalt oxide (ChMGOP-Co₃O₄). Analytical techniques furrier transform infra-red (FT-IR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to confirm the formation of ChMGOP-Co₃O₄. The effects of several experimental factors (solution pH, adsorbent dosage and coexisting ions) on the uptake of As(V) ions using ChMGOP-Co₃O₄ were examined through batch experiments. As(V) removal process was validated by experimentally and theoretically investigating the adsorption capacity, rate, and thermal effects. Thermodynamic parameters such as free energy (ΔG°), entropy (ΔS°) and enthalpy (ΔH°) were also calculated and were used to explain the mechanism of adsorption. Based on the results, the sorbent showed a high adsorption capacities (90.91 mg/g) at favorable neutral pH and superior removal efficiencies as high as 89% within 50 min. In addition, the adsorption isotherm followed the Langmuir isotherm in compare to the Freundlich, due to its higher R² value (0.992 < 0.941). Meanwhile, the kinetic data revealed that the of As(V) adsorption was controlled by pseudo-second-order. Overall, the adsorption mechanism studies revealed a spontaneous endothermic nature with predominance of physisorption over chemisorption. This study indicated that ChMGOP-Co₃O₄ is an exceptional novel adsorbent material for the efficient isolation of As(V) from aqueous media.

Laccase producing bacteria influenced the high decolorization of textile azo dyes with advanced study

Recent year, bacterial laccases are increasing interest in the field of industry and environmental applications especially decolorization of azo dyes. In industry, the dyes are present in stable nature including chemicals and lights. Due to these defects, the novel approaches are needed to removal of dyes before discharging into the environment. Among the various technologies, biological treatment methods and their strategies are very important, because of the decolorization and detoxification. Consecutively, biological mediated dyes removal are emerged with high potential especially microbes. Microbial laccases creates up new opportunities for their commercial applications. In this study, laccases were produced from Bacillus cereus (B. Cereus) and Pseudomonas parafulva (P. parafulva) by sub merged fermentation. For immobilization, the produced laccases were subjected to purify using 80% saturated ammonium sulphate and followed by dialysis. Then, crude laccases were immobilized through copper-alginate entrapment method. The maximum immobilized enzyme activity of the immobilized laccases were shown pH 8 at 50 °C and pH 7 at 40 °C for B. Cereus and P. parafulva respectively. In contrast, the normal enzyme activity was pH 10 at 40 °C and pH 8 at 40 °C were indicated for Bacillus cereus and P. parafulva respectively. Next, the free and immobilized laccases were performed the decolorization of three azo dyes T-blue, yellow GR and orange 3R, and exhibited that the 91.69 and 89.21% of Orange 3R were completely decolorized by both the B. Cereus and P. parafulva laccases when compared with free laccases enzymes. The confirmation of decolorization was monitored by UV-vis spectroscopy and FTIR spectroscopy, which clearly confirm the changes of peaks when compared with normal laccases. Finally, we have concluded that the B. Cereus and P. parafulva laccases are very important in azo dye decolorization and these used in future biological treatment of dyeing effluents.

Photoreduction of CO2 to CH4 over Efficient Z-Scheme γ-Fe2O3/g-C3N4 Composites

A series of composite γ-Fe₂O₃/g-C₃N₄ (denoted as xFeCN with x equal 5, 10, 15, and 20 of γ-Fe₂O₃ percentage in weight) was prepared by calcination and precipitation-impregnation methods. X-ray diffraction (XRD), Fourier transform infrared (FTIR), and X-ray photoelectron spectrometry (XPS) characterizations indicated the successful synthesis of Z-scheme FeCN composites. A red shift of the light absorption region was revealed by UV-vis diffuse reflectance spectroscopy (UV-DRS). In addition, photoluminescence spectroscopy (PL) spectra showed an interface interaction of two phases Fe₂O₃ and g-C₃N₄ in the synthesized composites that improved the charge transfer capacity. The photocatalytic activity of these materials was studied in the photoreduction of CO₂ with H₂O as the reductant in the gaseous phase. The composites exhibited excellent photoactivity compared to undoped g-C₃N₄. The CH₄ production rate over 10FeCN and 15FeCN composites (2.8 × 10^-2 and 2.9 × 10^-2 μmol h^-1 g^-1, respectively) was ca. 7 times higher than that over pristine g-C₃N₄ (0.4 × 10^-2 μmol h^-1 g^-1). This outstanding photocatalytic property of these composites was explained by the light absorption expansion and the prevention of photogenerated electron-hole pairs recombination due to its Z-scheme structure.

Detection of trizole contaminated waste water using biocatalyst and effective biodegradation potential of flubendiamide

Flubendiamide is a new class of chemical pesticide with broad spectrum activity against lepidopteran pests. Due to limited approach and high specificity towards various non targeted organisms, the unrestricted application of this pesticide as a prominent alternate for organochlorine and organophosphate pesticides, causing serious environmental pollution. In this study, wastewater was used for the determination of microbial strains and pesticide degrading fungi. Microbial population and flubendiamide resistant fungal strains were characterized using enriched medium. Aerobic bacteria (6.38 ± 0.23 log CFU/mL), nitrifying bacteria (2.73 ± 0.31 CFU/mL), Lactobaillus (0.72 ± 0.03 log CFU/mL), actinomycetes (5.36 ± 0.27 log CFU/mL) and fungi (4.79 ± 0.22 log CFU/mL) were detected. The prominent fungi genera were, Fusarium, Trichoderma, Cladophialophora, Paecilomyces, Talaromyces, Penicillium, Aspergillus, Candida, Phyllosticta, Mycosphaerella, Ochroconis, and Mucor. Minimum inhibitory concentration of the rapidly growing organism (FR04) revealed its ability to tolerate up to 1250 mg/L flubendiamide concentration. Morphological, biochemical and molecular analysis revealed that the strain was Aspergillus terreus FR04. The residual pesticide was detected using a High Performance Liquid Chromatography (HPLC). High performance liquid chromatography analysis revealed that 89 ± 1.9% pesticide removal efficiency was observed in strain FR04 at optimized culture conditions (96 h, pH 6.5, 30 °C and 300 mg/L pesticide concentration). The strain FR04 degraded pollutants from the wastewater and improved water quality. A. terreu sFR04 is an indigenous fungus and has the ability to degrade trizole pesticides from the wastewater significantly.

Photocatalytic degradation of organic synthetic dyes and textile dyeing waste water by Al and F co-doped TiO2 nanoparticles

Textile wastewater threatens people health by alluring diseases and revealing public existing close to the waste to the dangerous products within. Because waste causes a risk to the environment and people, waste management making is the main challenge of the municipal world. Environmental process such as toxic dye degradation can be stepped up through photochemical process such as visible light induced catalytic degradation. Here, the successful synthesis of co-doping of Al and F into TiO2 nanoparticles (Al-F∕TiO2 NPs) by solid state reaction method comprising different proportions of co-dopants is evaluated for the applications of degrading organic synthetic dyes and textile dyeing waste water. Influence of co-dopants was studied in their optical, structural, compositional, morphological and vibrational properties. The average crystallite size of Al-F∕TiO2 NPs was found as 15 nm.FTIR and UV-vis spectrum confirmed F and Al atoms were incorporated into the TiO2 lattice.The absorption edges slightly moved to shorter wavelength by increasing level of dopants and this specifies the control of optical absorption of TiO2 by the incorporation of F and Al3+ ions.The EDS spectrum indicates the purity of the samples. The highest zone of inhibition for the prepared nanoparticles over Staphylococcus aureus reached to 22 mm. The rate constant (kapp) value of MB, MO and textile waste water is 0.0138/min, 0.0174/min and 0.0139/min for the prepared nanoparticles respectively. The study of photocatalytic degradation of visible light assisted MB, MO and real textile waste water by Al-F∕TiO2 NPs revealed that the prepared nanoparticles act as ideal catalyst by tuning the concentration of co-dopants in TiO2.

Hexavalent chromium removal from aqueous solutions using biogenic iron nanoparticles: Kinetics and equilibrium study

Green mediated biosynthesis of iron oxide nanoparticles utilising Rosa indica flower petal extracts (RIFP-FeONPs) was used in this investigation. The RIFP-FeONPs were evaluated by the UV-Visible Spectroscopy, FTIR, SEM, EDX, XRD, Zeta potentials, and DLS, and been engaged than for the elimination of Cr (VI) from the contaminated environments. At 269 nm, the RIFP-FeONPs surface plasmon vibration bands were observed, which attributed to the Fe³⁺. XRD patterns of RIFP-FeONPs depicted the intense diffraction peak of face-centered cubic (fcc) iron at a 2θ value of 45.33° from the (311) lattice plane indisputably revealed that the particles are constituted of pure iron. The fabricated nanomaterials are spherical and polydisperse with a diameter of 70-120 nm, and various agglomeration clusters are attributable to intermolecular interaction. Zeta potential measurement and particle size distribution of RIFP-FeONPs showed a mean average size of 115.5 ± 29 nm and a polydispersity index (PDI) of 0.420. The study aims to analyse the appropriateness of RIFP-FeONPs for removing hexavalent chromium from the aqueous environment and the application of adsorption isotherm and statistical models in the experiment. The sorption of Cr (VI) on RIFP-FeONPs was observed to fit well with the isothermal models (R² = 0.98). The linear correlation between processing parameters and time demonstrated that the adsorption efficiency of Cr (VI) well correlated with the pseudo-first order kinetic model and isothermal adsorption with the Langmuir and Freundlich isothermal models, so that the RIFP-FeONPs could be a prospective nanosorbent for hexavalent chromium removal from industrial waste.

Effect of Ag doped MnO2 nanostructures suitable for wastewater treatment and other environmental pollutant applications

A modest sol-gel method has been employed to prepare the pure and Ag doped MnO2 nanoparticles and methodologically studied their physical, morphological, and photosensitive properties through XRD, TEM, EDAX, Raman, UV, PL and N2 adsorption - desorption study. Tetragonal crystalline arrangement with spherical nanoparticles was found out through XRD and TEM studies. The EDAX studies further supported that formation Ag in the MnO2 crystal matrix. The bandgap energy of Ag doped MnO2 was absorbed through UV spectra. Photo -generated recombination process and surface related defects were further recognized by PL spectra. Through visible light irradiation, the photo - degradation of methyl orange (MO) and phenol dye solutions were observed. The optimum condition of (10 wt% of Ag) Ag doped MnO2 catalyst showed tremendous photocatalytic efficiency towards MO than phenol under same experimental study.

Improved visible light photocatalytic degradation of yttrium doped NiMgAl layered triple hydroxides for the effective removal of methylene blue dye

Fabrication of layered triple hydroxides (LTH) is a typical and remarkable approach to produce new functionalities passionately investigated for photocatalytic removal of organic pollutants from industrial wastewater. The hydrothermal method was used to prepare different weight percentages of yttrium (Y) doped NiMgAl LTH. The structural, functional, optical, and morphological properties of the prepared samples were investigated using X-ray diffraction, Fourier transformed-infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and scanning electron microscopy. The photocatalytic degradation of the different percentages of Y-doped LTH samples were assessed through the photocatalytic degradation of methylene blue dye under the visible light irradiation. When compared to other lower concentrations of Y doping, the photocatalytic degradation efficiency of 1 wt.% Y-doped LTH was higher. Thus, the optimized LTH's improved photocatalytic performance was attributed to increased visible light absorption with low transmission and improved electron-hole separation.

Effective removal of heavy metals in industrial wastewater with novel bioactive catalyst enabling hybrid approach

Recent years, heavy metal reduction of contaminated atmosphere using microbes is heightened worldwide. In this context, the current study was focused on heavy metal resistant actinomycete strains were screened from effluent mixed contaminated soil samples. Based on the phenotypic and molecular identification, the high metal resistant actinomycete strain was named as Nocardiopsis dassonvillei (MH900216). The highest bioflocculent and exopolysaccharide productions of Nocardiopsis dassonvillei (MH900216) was confirmed by various invitro experiments result. The heavy metal degrading substances was characterized and effectively confirmed by Fourier transform infrared spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning electron microscope (SEM). Further, the heavy metal sorption ability of actinomycete substances bioflocculent was exhibited 85.20%, 89.40%, 75.60%, and 51.40% against Cd, Cr, Pb and Hg respectively. Altogether, the bioflocculent produced actinomycete Nocardiopsis dassonvillei (MH900216) as an excellent biological source for heavy metal reduction in waste water, and it is an alternative method for effective removal of heavy metals towards sustainable environmental management.

Effective degradation of Chlortetracycline using dual bio catalyst

Chlortetracycline (CTC) degradation using potential microbial consortia or individual bacterial strains was useful method for improving bioremediation potential. The co-culture (Klebsiella pneumoniae CH3 and Bacillus amyloliquefaciens CS1) of bacterial strains have the ability to degrade chlortetracycline (91.8 ± 1.7%), followed by sulfamethoxazole (62.1 ± 1.2%) and amoxicillin (73.9 ± 3.3%). It was observed that the degradation potential was maximum after 10 days incubation, 8-10% inoculum, pH 7.5, and antibiotic concentration ranged from 150 to 200 mg/L. The initial concentrations of CTC significantly affected CTC degradation. In strain CH3, maximum biodegradation of CTC (99.4 ± 2.3%) was observed at 200 mg/L initial CTC concentrations. In CS1, maximum biodegradation of CTC was obtained at 150 mg/L concentration (80.5 ± 3.2%) after 10 days of culture. Alkaline pH was found to be suitable for the degradation of antibiotic than acidic range. After initial optimization by one factor at a time approach in free cells, the bacterial strains (CH3 and CS1) were co-immobilized. The co-immobilized bacterial cells showed improved degradation potential than free cells. To determine the biodegradation potential of immobilized cells, the selected strains were immobilized in polymer beads and treated with CTC with 175 mg/L initial concentration. The experimental results revealed that after 3 days of treatment the residual CTC concentration was 150.1 ± 3.2 mg/L and it decreased as 1.28 ± 0.01 mg/L after 10 days of treatment. The present study confirmed the effectiveness and feasibility of biodegradation ability of K. pneumoniae CH3 and B. amyloliquefaciens CS1 immobilized for CTC degradation in wastewater.

Statistical optimization of silver nanoparticle synthesis by green tea extract and its efficacy on colorimetric detection of mercury from industrial waste water

For the optimization of silver nanoparticle production, a central composite design was used with three parameters: AgNO₃ concentration, green tea extract concentration, and temperature at three different levels. The size of the synthesized silver nanoparticle, its UV absorbance, zeta potential, and polydispersity index were set as the response parameters. Silver nanoparticles obtained in the optimization process were characterized and its efficacy on colorimetric detection of mercury was evaluated. The response variables were significant for the factors analyzed, and each variable had a significant model (P < 0.05). The ideal conditions were: 1 mM AgNO₃, 0.5% green tea extract, and 80 °C temperature. To analyze the produced AgNPs under certain ideal conditions, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used. The UV-visible spectra of AgNPs revealed an absorption maxima at 424 nm. The XRD pattern reveals a significant diffraction peak at 38.25°, 44.26°, 64.43°, and 77.49°, which corresponds to the (111), (200), (220), and (311) planes of polycrystalline face-centered cubic (fcc) silver, respectively. The TEM and SEM analyses confirmed that the particles were spherical, and dynamic light scattering study determined the average diameter of AgNPs to be 77.4 nm. The AgNPs have a zeta potential of -62.6 mV, as determined by the zeta sizer analysis. The AgNPs detects mercury at a micromolar concentration. Furthermore, the environmentally friendly generated AgNPs were used to detect mercury in a colorimetric method that was effectively employed for analytical detection of Hg²⁺ ions in an aqueous environment for the purpose of practical application.

Fabrication of graphene oxide-p-phenylenediamine nanocomposites as fluorescent chemosensors for detection of metal ions

In this work, graphene oxide-p-Phenylenediamine nanocomposites of two different ratios of Graphene oxide: p-Phenylenediamine (1:1 and 1:5) were prepared and characterized by using analytical, spectroscopic and microscopic studies (GO-pPD 11 and GO-pPD 15). These nanocomposites were employed as fluorescent chemosensors for sensing potential cations. Remarkably, graphene oxide-p-Phenylenediamine nanocomposites of ratio 1:1 (GO-pPD 15) was selective and sensitive to Ag⁺ ions, whereas the graphene oxide-p-Phenylenediamine nanocomposites of ratio 1:5 (GO-pPD 15) was selective to Ce³⁺ions. A possible mechanism as switch "off-on" is proposed built on the inhibition of the photo induced electron transfer process in both the fluorescent probes in detecting the metal ions. In addition, interference studies were performed with the help of competitive complexation analysis and no significant interference were found by other potentially competing cations. The pH studies revealed that both the chemosensors can be used at the physiological pH for the ion detection and also the detection time was within 2-3 min. Both the chemosensors show good reversibility and hence the sensors can be used for multiple times. The newer nanocomposites were then utilized in the real water sample analysis as to check its real level application purpose.

Knowledge extraction of sonophotocatalytic treatment for acid blue 113 dye removal by artificial neural networks

Removing decolorizing acid blue 113 (AB113) dye from textile wastewater is challenging due to its high stability and resistance to removal. In this study, we used an artificial neural network (ANN) model to estimate the effect of five different variables on AB113 dye removal in the sonophotocatalytic process. The five variables considered were reaction time (5-25 min), pH (3-11), ZnO dosage (0.2-1.0 g/L), ultrasonic power (100-300 W/L), and persulphate dosage (0.2-3 mmol/L). The most effective model had a 5-7-1 architecture, with an average deviation of 0.44 and R² of 0.99. A sensitivity analysis was used to analyze the impact of different process variables on removal efficiency and to identify the most effective variable settings for maximum dye removal. Then, an imaginary sonophotocatalytic system was created to measure the quantitative impact of other process parameters on AB113 dye removal. The optimum process parameters for maximum AB 113 removal were identified as 6.2 pH, 25 min reaction time, 300 W/L ultrasonic power, 1.0 g/L ZnO dosage, and 2.54 mmol/L persulfate dosage. The model created was able to identify trends in dye removal and can contribute to future experiments.

Effect of Ca2+ ions on naphthalene adsorption/desorption onto calcium oxide nanoparticle: Adsorption isotherm, kinetics and regeneration studies

The adsorptive nature of calcium oxide nanoparticles in aqueous sample of naphthalene in presence of Ca²⁺ ions was estimated. Enhanced efficiency of calcium oxide regeneration (90%) with the aid of calcium chloride in the solution concentration of 0.002-0.1 M was depicted. The less degree of toxic naphthalene desorption merged with SEM, FTIR and XRD characterization data portrays the importance of naphthalene adsorption onto calcium oxide using calcium chloride for regeneration. Batch adsorption studies were performed to evaluate the operating parameters such as pH, naphthalene concentration, contact time and impact of Ca²⁺ on naphthalene study. The adsorption isotherm of naphthalene on calcium oxide nanoparticle was described by Langmuir, Freundlich, Temkin and Dubinin Radushkevich and theoretical maximum monolayer adsorption capacity was found to be 63.81 mg/g at 303 K. The adsorption kinetic best fitted with pseudo second order kinetic model. The positive influence of making the addition of Ca²⁺ ions into naphthalene solution for its rapid adsorption was elucidated which is leaded by a probable increase in sorption capacity for naphthalene molecules at lower concentrations. The stable nature of crystallinity of calcium oxide and a less degree of naphthalene molecules leaching during consecutive cycles of adsorptive process and nanoparticle regeneration was also scrutinized.

Synthesis and Characterization of an α-Fe2O3-Decorated g-C3N4 Heterostructure for the Photocatalytic Removal of MO

This study describes the preparation of graphitic carbon nitride (g-C3N4), hematite (α-Fe2O3), and their g-C3N4/α-Fe2O3 heterostructure for the photocatalytic removal of methyl orange (MO) under visible light illumination. The facile hydrothermal approach was utilized for the preparation of the nanomaterials. Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray (EDX), and Brunauer-Emmett-Teller (BET) were carried out to study the physiochemical and optoelectronic properties of all the synthesized photocatalysts. Based on the X-ray photoelectron spectroscopy (XPS) and UV-visible diffuse reflectance (DRS) results, an energy level diagram vs. SHE was established. The acquired results indicated that the nanocomposite exhibited a type-II heterojunction and degraded the MO dye by 97%. The degradation ability of the nanocomposite was higher than that of pristine g-C3N4 (41%) and α-Fe2O3 (30%) photocatalysts under 300 min of light irradiation. The formation of a type-II heterostructure with desirable band alignment and band edge positions for efficient interfacial charge carrier separation along with a larger specific surface area was collectively responsible for the higher photocatalytic efficiency of the g-C3N4/α-Fe2O3 nanocomposite. The mechanism of the nanocomposite was also studied through results obtained from UV-vis and XPS analyses. A reactive species trapping experiment confirmed the involvement of the superoxide radical anion (O2•-) as the key reactive oxygen species for MO removal. The degradation kinetics were also monitored, and the reaction was observed to be pseudo-first order. Moreover, the sustainability of the photocatalyst was also investigated.

Current advancements on the fabrication, modification, and industrial application of zinc oxide as photocatalyst in the removal of organic and inorganic contaminants in aquatic systems

Industrial wastewaters contain hazardous contaminants that pollute the environment and cause socioeconomic problems, thus demanding the employment of effective remediation procedures such as photocatalysis. Zinc oxide (ZnO) nanomaterials have emerged to be a promising photocatalyst for the removal of pollutants in wastewater owing to their excellent and attractive characteristics. The dynamic tunable features of ZnO allow a wide range of functionalization for enhanced photocatalytic efficiency. The current review summarizes the recent advances in the fabrication, modification, and industrial application of ZnO photocatalyst based on the analysis of the latest studies, including the following aspects: (1) overview on the properties, structures, and features of ZnO, (2) employment of dopants, heterojunction, and immobilization techniques for improved photodegradation performance, (3) applicability of suspended and immobilized photocatalytic systems, (4) application of ZnO hybrids for the removal of various types of hazardous pollutants from different wastewater sources in industries, and (5) potential of bio-inspired ZnO hybrid nanomaterials for photocatalytic applications using renewable and biodegradable resources for greener photocatalytic technologies. In addition, the knowledge gap in this field of work is also highlighted.

A state-of-the-art review on microbial desalination cells

The rapid growth in population has increased the demand for potable water. Available technologies for its generation are the desalination of sea water through reverse osmosis, electrodialysis etc., which are energy and cost intensive. In this context, microbial desalination cell (MDC) presents a low-cost and sustainable option which can simultaneously treat wastewater, desalinate saline water, produce electrical energy and recover nutrients from wastewater. This review paper is focussed on presenting a detailed analysis of MDCs starting from the principle of operation, microbial community analysis, basic architecture, evolution in design, operational challenges, effect of process parameters, scale-up studies, application in multiple arenas and future prospects. After thorough review, it can be inferred that MDCs can be used as a stand-alone option or pre-treatment step for conventional desalination techniques without the application of external energy. MDCs have been used in multiple applications ranging from desalination, remediation of contaminated water, recovery of energy and nutrients from wastewater, softening of hardwater, biohydrogen production to degradation of waste engine oil. Although, MDCs have been used for multiple applications, still a number of operational challenges have been reported viz., interference of co-existing ions during desalination, membrane fouling, pH imbalance and limited potential of exoelectrogens. However, the re-circulation of anolytes with electrodialysis chamber has led to the maintenance of optimal pH for favourable microbial growth leading to improvement in the overall performance of MDCs. In future, genetic engineering may be used for improving the electrogenic activity of microbial community, next generation materials may be used as anode and cathode, varied sources of wastewater may be explored as anolytes, life cycle analysis and exergy analysis may be carried out to study the impact on environment and detailed pilot scale studies have to be carried out for assessing the feasibility of operation at large scale.

Supercritical Technology-Based Date Sugar Powder Production: Process Modeling and Simulation

Date palm fruits (Phoenix dactylifera) contain high levels of fructose and glucose sugars. These natural sugar forms are healthy, nutritional and easily assimilate into human metabolism. The successful production of soluble date sugar powder from nutritious date fruits would result in a new food product that could replace the commercial refined sugar. In this work, a novel process technology based on the supercritical extraction of sugar components from date pulp was modeled and simulated using Aspen Plus software. The process model consisted of three main steps that were individually simulated for their optimal working conditions as follows: (a) freeze-drying of the date pulp at −42 °C and 0.0001 bar; (b) supercritical extraction of the sugar components using a 6.77 wt.% water mixed CO2 solvent system at a pressure of 308 bar, temperature of 65 °C, and CO2 flow rate of 31,000 kg/h; and (c) spray-drying of the extract using 40 wt.% Gum Arabic as the carrier agent and air as drying medium at 150 °C. The overall production yield of the process showed an extraction efficiency of 99.1% for the recovery of total reducing sugars from the date fruit. The solubility of the as-produced date sugar powder was improved by the process selectivity, elimination of insoluble fiber contents, and the addition of Gum Arabic. The solubility of the final date sugar product was estimated as 0.89 g/g water.

A 2D/1D heterojunction nanocomposite built from polymeric carbon nitride and MIL-88A(Fe) derived α-Fe2O3 for enhanced photocatalytic degradation of rhodamine B

2D/1D heterojunction α-Fe2O3/C3N4 photocatalysts containing α-Fe2O3 microrods and polymeric carbon nitride flakes are synthesised through the calcination of Fe-based metal-organic frameworks and boost the visible light photocatalytic degradation of rhodamine B.

Impact of dysprosium doped (Dy) zinc ferrite (ZnFe2o4) nanocrystals in photo- fenton exclusion of recalcitrant organic pollutant

The issue of effluent, especially organic colorants from several manufacturing units overlays an immense delinquent of the current epoch owing to its effect on oncogenic health hazards. Thus, Rare Earth Metal dysprosium (Dy) doped Zinc Ferrite (ZnFe₂O₄) were as-synthesized by a facile co-precipitation technique as an effectual nano photocatalyst intended to the amputation of these noxious dyes. The structural, functional, optical, magnetic, and degradation properties of this RE (Dy³⁺) doped ions were investigated using various characterizations, such as crystallite size (D) and several parameters (cation distribution, oxygen positional parameters, and bond length) were determined using XRD (X-ray diffraction) and it was found that as the dy³⁺ ion concentration increases the speck size decreased and the grain size remained within nano regime, which intern affects the surface area. From BET analysis it was found that on increasing the doping concentration, the surface area increases which pave a substantial role in the photo-Fenton activity. By using FT-IR (Fourier-transform infrared spectroscopy) various functional parameters (elastic, interionic bonds, ion distribution, etc.) were determined. Raman spectra had no extra peak formation which is seen to have pure phase formation of the as-synthesized samples. HR-TEM (High-Resolution Transmission Electron Microscopy analysis were done to determine the nature of the sample, the as-synthesized magnetic samples exhibit a polycrystalline formation with cubical agglomeration. The magnetic property was very significant for x = 0.10 concentration. As-synthesized (Fe_0.9064Zn_0.0936) [Fe_1.0936Dy_0.1Zn_0.8064] O₄) exhibits a momentous photo - Fenton activity against MB (Methylene blue), its removal efficiency was found to be 97.3% after 45 min. Also, this spinel ferrite acts as a magnetic recyclable catalyst even after 5 cycles with an insignificant lessening of elements and photo-Fenton activity.

Mechanochemical synthesis of ternary heterojunctions TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 for effective charge separation in semiconductor photocatalysis: A comparative study

TiO₂, ZnO, and SnO₂ metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO₂ with either ZnO or SnO₂ in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO₂ from anatase to rutile and yields ternary heterojunction of the type TiO₂(A)/TiO₂(R)/ZnO and TiO₂(A)/TiO₂(R)/SnO₂ (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO₂(A)/TiO₂(R)/ZnO heterojunction is attributed to the formation of Ti³⁺-V_o defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO₂ and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti⁴⁺ and Zn²⁺. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.

Hydrogen production via water splitting over graphitic carbon nitride (g-C3N4 )-based photocatalysis

Photocatalytic splitting of water into hydrogen and oxygen using semiconductor photocatalysts and light irradiation has been attracted much attention and considered to be an alternative for nonrenewable fossil fuel to solve environmental problems and energy crisis and also an as promising approach to produce clean, renewable hydrogen fuel. Owing to their various advantages such as low cost and environmental friendly, chemical, and thermal stability, appropriate band structure, graphitic carbon nitride (g-C3N4 ) photocatalysts have gained multitudinous attention because of their great potential in solar fuels production and environmental remediation. However, due to its fast charge carrier’s recombination, low surface, and limited absorption of the visible light restrict their activity toward hydrogen evolution and numerous modification techniques were applied to solve these problems such as structural modification, metal/nonmetal doping, and noble metal loading, and coupling semiconductors. In this chapter, we summarize recent progress in the synthesis and characterization of the g-C3N4-based photocatalyst. Several modification methods used to enhance the photocatalytic hydrogen production of g-C3N4-based photocatalyst were also highlighted. This chapter ends with the future research and challenges of hydrogen production over g-C3N4-based photocatalyst.

Recent advancements of g-C3N4-based magnetic photocatalysts towards the degradation of organic pollutants: a review

Heterogeneous photocatalysis premised on advanced oxidation processes has witnessed a broad application perspective, including water purification and environmental remediation. In particular, the graphitic carbon nitride (g-C₃N₄), an earth-abundant metal-free conjugated polymer, has acquired extensive application scope and interdisciplinary consideration owing to its outstanding structural and physicochemical properties. However, several issues such as the high recombination rate of the photo-generated electron-hole pairs, smaller specific surface area, and lower electrical conductivity curtail the catalytic efficacy of bulk g-C₃N₄. Another challenging task is separating the catalyst from the reaction medium, limiting their reusability and practical applications. Therefore, several methodologies are adopted strategically to tackle these issues. Attention is being paid, especially to the magnetic nanocomposites (NCs) based catalysts to enhance efficiency and proficient reusability property. This review summarizes the latest progress related to the design and development of magnetic g-C₃N₄-based NCs and their utilization in photocatalytic systems. The usefulness of the semiconductor heterojunctions on the catalytic activity, working mechanism, and degradation of pollutants are discussed in detail. The major challenges and prospects of using magnetic g-C₃N₄-based NCs for photocatalytic applications are highlighted in this report.

Ionic Porous Aromatic Framework as a Self-Degraded Template for the Synthesis of a Magnetic γ-Fe2O3/WO3·0.5H2O Hybrid Nanostructure with Enhanced Photocatalytic Property

An ionic porous aromatic framework is developed as a self-degraded template to synthesize the magnetic heterostructure of γ-Fe₂O₃/WO₃·0.5H₂O. The Fe₃O₄ polyhedron was obtained with the two-phase method first and then reacted with sodium tungstate to form the γ-Fe₂O₃/WO₃·0.5H₂O hybrid nanostructure. Under the induction effect of the ionic porous network, the Fe₃O₄ phase transformed to the γ-Fe₂O₃ state and complexed with WO₃·0.5H₂O to form the n-n heterostructure with the n-type WO₃·0.5H₂O on the surface of n-type γ-Fe₂O₃. Based on a UV-Visible analysis, the magnetic photocatalyst was shown to have a suitable band gap for the catalytic degradation of organic pollutants. Under irradiation, the resulting γ-Fe₂O₃/WO₃·0.5H₂O sample exhibited a removal efficiency of 95% for RhB in 100 min. The charge transfer mechanism was also studied. After the degradation process, the dispersed powder can be easily separated from the suspension by applying an external magnetic field. The catalytic activity displayed no significant decrease after five recycles. The results present new insights for preparing a hybrid nanostructure photocatalyst and its potential application in harmful pollutant degradation.

In-situ thermal phase transition and structural investigation of ferroelectric tetragonal barium titanate nanopowders with pseudo-cubic phase

Optimization and miniaturization of existing electronic devices require the development of advanced nanostructured materials with high phase and structural purity. Over the past decade, barium titanate (BaTiO₃) has attracted considerable attention due to its outstanding ferroelectric and dielectric properties. The present study involved the investigation of the phase transition and structural stability of tetragonal BaTiO₃ nanopowders with pseudo-cubic phase using an in-situ high resolution and high temperature X-ray diffraction method. Under ambient conditions, the coexistence the tetragonal and cubic phases with weight fractions of 75.7% and 24.3%, respectively, was determined in BaTiO₃. In the temperature range of 25 °C-300 °C, phase boundaries of BaTiO₃ (180 nm in size) exhibiting several phases were detected. The phase transformation behavior, relative crystal phase content, lattice parameters, crystallite size, and tetragonality of the BaTiO₃ nanopowders were established by the Rietveld refinement method at the onset temperature from 25 °C to 300 °C. Up to 150 °C, the nanopowders exhibited a complete transition of the cubic phase. Additionally, a complete tetragonal to cubic transformation was accomplished by a decrease of tetragonality at 125 °C and an increase in the crystallite size at 300 °C.

Synthesis and characterization of magnetite carbon nanocomposite from agro waste as chromium adsorbent for effluent treatment

The waste water released from industries which contain pollutants like heavy metals, dyes and other toxic chemicals brings numerous harms to the ecosystem and humans. Nowadays the nanocomposites based technologies are effectively used for environmental remediation. In the present study, hexavalent chromium was removed from the industrial effluent using magnetite carbon nanocomposite. The nanocomposite composed of highly porous carbon and iron oxide nanoparticles prepared by using agrowastes (sugarcane bagasse and orange peel extract). Iron oxide nanoparticles (FeONPs) formation was confirmed by UV-visible spectroscopy; incorporation of magnetite with highly porous carbon was established by Fourier Transforms Infrared Spectroscopy and X-ray Diffraction Spectroscopy. Morphological features of magnetite nanoparticles and highly porous carbon were analyzed using Scanning Electron Microscope and Transmission Electron Microscope. Magnetic properties analyzed by Vibrating Sample Magnetometer revealed magnetite carbon nanocomposite exhibited better Ms value than highly porous carbon. The concentration of Cr⁶⁺ in treated effluent was determined using Atomic Absorption Spectroscopy. Pseudo-second order equation fitted with kinetics and the Langmuir monolayer favors for isotherm. This study reveals efficiency in Cr⁶⁺ removal from effluent using magnetite carbon nanocomposites which extends their application in waste water treatment.

Au integrated 2D ZnO heterostructures as robust visible light photocatalysts

Integration of semiconducting nanostructures with noble metal nanoparticles are turning highly desirable for cost efficient energy and environmental related applications. From this viewpoint, we report on a facile aqueous synthesis of polymer capped gold (Au) nanoparticles on free standing 2D layered structures of zinc oxide (ZnO) to result with ZnO/Au nanocomposites. Concentration of Au nanoparticles were observed to promote the preferential growth of ZnO along the (002) wurtzite plane. The ZnO/Au structures and their morphological dissemination was noted to be of few. This flake like structure was also noted to be greatly influenced by the concentration of Au in the colloidal blend. Optical band edge transformations noted in the absorption spectra across the lower wavelength region and the shift in surface plasmon resonance (SPR) towards the red region of the visible spectrum signify the improved absorptivity of the heterostructures along the visible spectrum. These heterostructures exhibited remarkable visible light driven photocatalytic activity (99% efficiency) on par with pristine ZnO. The findings also attest this new class of composite structures to open up new openings in diversified solar energy conversion related functions.