Clay-polymer nanocomposites for effective water treatment: opportunities, challenges, and future prospects.

The metal intoxication and its associated adverse effects to humans have led to the research for development of water treatment technologies from pollution hazards. Therefore, development of cheaper water remediation technologies is more urgent than ever. Clays and clay minerals are naturally occurring, inexpensive, non-toxic materials possessing interesting chemical and physical properties. As a result of interesting surface properties, these have been developed as efficient absorbent in water remediation. Recently, clay-polymer nanocomposites have provided a cost-effective technological platform for removing contaminants from water. Covering research advancements from past 25 years, this review highlights the developments in clay-polymer nanocomposites and their advanced technical applications are evaluated with respect to the background and issues in remediation of toxic metals and organic compounds from water. The extensive analysis of literature survey of more than two decades suggests that future work need to highlight on advancement of green and cost-effective technologies. The development of understanding of the interaction and exchange between toxin and clay-polymer composites would provide new assembly methods of nanocomposites with functional molecules or nanomaterials need to be extended to increase the detection and extraction limit to parts per trillion.

Biogenic synthesis of iron oxide nanoparticles using leaf extract of Spilanthes acmella: antioxidation potential and adsorptive removal of heavy metal ions.

The sequestration of contaminants from wastewater, such as heavy metals, has become a major global issue. Multiple technologies have been developed to address this issue. Nanotechnology is attracting significant interest as a new technology, and numerous nanomaterials have been produced for sequestrating heavy metals from polluted water due to their superior properties arising from the nanoscale effect. This study reports biosynthesis of iron oxide nanoparticles (IO-NPs) and their applications for adsorptive sequestration of various metal ions from aqueous solutions. Biosynthesis of IO-NPs has been carried out by using leaf extract of Spilanthes acmella, a medicinal plant. FTIR analysis of the leaf extract and biosynthesized IO-NPs marked the role of various functional groups in biosynthesis of IO-NPs. FESEM analysis revealed the average size range of IO-NPs as 50 to 80 nm, while polydisperse nature was confirmed by DLS analysis. EDX analysis revealed the presence of Fe, O, and C atoms in the elemental composition of the NPs. The antioxidant potential of the biosynthesized IO-NPs (IC50 = 136.84 µg/mL) was confirmed by DPPH assay. IO-NPs were also used for the adsorptive removal of As3+, Co2+, Cd2+, and Cu2+ ions from aqueous solutions with process optimization at an optimized pH (7.0) using dosage of IO-NPs as 0.6 g/L (As3+ and Co2+) and 0.8 g/L (Cd2+ and Cu2+). Adsorption isotherm analysis revealed the maximum adsorption efficiency for As3+ (21.83 mg/g) followed by Co2+ (20.43 mg/g), Cu2+ (15.29 mg/g), and Cd2+ (13.54 mg/g) using Langmuir isotherm model. The biosynthesized IO-NPs were equally efficient in the simultaneous sequestration of these heavy metal ions signifying their potential as effective nanoadsorbents.

Potential applications of green-synthesized iron oxide NPs for environmental remediation.

Water pollution is a significant issue worldwide due to an increase in anthropogenic activities. Heavy metals and dyes are among the most problematic contaminants that threaten the environment and negatively impact human health. Iron oxide nanoparticles (IONPs) synthesized using green methods have shown potential in these areas due to their significant adsorption capacity and photocatalytic potential. The size and morphology of biogenic IONPs can be tailored depending upon the concentration of the reducing medium and metal salt precursor. Green-synthesized IONPs have been found to be effective, economical, and environmentally friendly with their large surface area, making them suitable for removing toxic matter from contaminated water. Furthermore, they exhibit antibacterial potential against harmful microorganisms. The study emphasizes the importance of using such environmentally friendly tools to remove heavy metal ions and organic compounds from contaminated water. The underlying mechanism for the adsorption of heavy metal ions, photocatalytic degradation of organic compounds, and antimicrobial action has been explored in detail. The future prospective for the beneficial utilization of biogenic IONPs has also been signified to provide a detailed overview.

Adsorption and photodegradation of organic contaminants by silver nanoparticles: isotherms, kinetics, and computational analysis.

In view of the widespread and distribution of several classes and types of organic contaminants, increased efforts are needed to reduce their spread and subsequent environmental contamination. Although several remediation approaches are available, adsorption and photodegradation technologies are presented in this review as one of the best options because of their environmental friendliness, cost-effectiveness, accessibility, less selectivity, and wider scope of applications among others. The bandgap, particle size, surface area, electrical properties, thermal stability, reusability, chemical stability, and other properties of silver nanoparticles (AgNPS) are highlighted to account for their suitability in adsorption and photocatalytic applications, concerning organic contaminants. Literatures have been reviewed on the application of various AgNPS as adsorbent and photocatalyst in the remediation of several classes of organic contaminants. Theories of adsorption have also been outlined while photocatalysis is seen to have adsorption as the initial mechanism. Challenges facing the application of silver nanoparticles have also been highlighted and possible solutions have been presented. However, current information is dominated by applications on dyes and the view of the authors supports the need to strengthen the usefulness of AgNPS in adsorption and photodegradation of more classes of organic contaminants, especially emerging contaminants. We also encourage the simultaneous applications of adsorption and photodegradation to completely convert toxic wastes to harmless forms.

Zinc oxide nanoparticles adsorb emerging pollutants (glyphosate pesticide) from aqueous solutions.

The present study captures the precipitation synthesis of zinc nanoparticles and modification with alumina and oleic acid. The crystalline size evaluated from the XRD profile of the zinc oxide nanoparticles was 18.05 nm but was reduced to 14.20 and 14.50 nm upon modification with oleic acid and alumina. The XRD spectra also showed evidence of the amorphous nature of zinc oxide nanoparticles and subsequent enhancement upon modification. A porous appearance was observed in the SEM instrumentation but seems to be enhanced by modification. The FTIR absorption spectra of the nanoparticles showed a peak associated with ZnO vibration around 449 cm, but the enhanced intensity was observed due to modification. The prepared ZnO-NPs and the modified samples were good materials for the adsorption removal of glyphosate from water, recording efficiencies above 94% at neutral pH and showing a possible incremental trend with an enhanced period of contact and adsorbent dosage. The adsorbents showed maximum capacity that ranged from 82.85 to 82. 97 mg/g. The adsorption models of Freundlich, Temkin, Dubinin-Radushkevich and BET showed excellent fitness. Results from computational results complemented experimental data and were used to identify the sites for adsorption and characteristics of molecular descriptors for the systems.

Synthesis and application of novel microporous framework of nanocomposite from trona for photocatalysed degradation of methyl orange dye.

Photocatalysed degradation of environmental contaminants is one of the most fashionable technologies in the purification of water because the method converts toxic products to nontoxic ones. In this study, a method has been developed to synthesize novel nanocomposites of Na-Ca-Al-Si oxides for the first time. The average surface area, pore volume and pore size for the novel product were 1742.55 m2/g, 0.3499 cc/g and 3.197 nm respectively. The crystal parameters were a = 7.1580 Å, b = 7.4520 Å, c = 7.7160 Å, α = 115.0600, ß = 107.3220, γ = 100.4380, density (calculated) = 2.0 × 103g/cm3 and cell volume = 332.7 Å3 respectively. The average crystalline size deduced from the Scherrer equation (i.e. 6.9393 nm) was higher than the value of 1.024 nm obtained from the graphical method. The FTIR and UV spectra of the nanocomposites were unique and provided baseline information that characterises the new product. XRD profiling of the new product reveals the existent of a silica framework consisting of NaAlSi3O3 and CaAl2Si2O8 The synthesized nanocomposites is an effective photocatalyst for the degradation of methyl orange dye in water, with aoptimum efficiency of 96% at an initial dye concentration of 10 ppm, the adsorbent dosage of 0.5 g,contact time of 90 min and pH of 2.5. The Langmuir-Hinshelwood, modified Freundlich and pseudo-second kinetic models were significant in the description of the photocatalytic kinetics of the degraded dye molecules.

A Brief Review on Fruit and Vegetable Extracts as Corrosion Inhibitors in Acidic Environments.

The corrosion of metals, i.e., the initiation and acceleration of the surface deterioration of metals through an electrochemical reaction with the surrounding intrusive environment, is a global concern because of the economic and environmental impacts. Corrosion inhibitors are considered the most practical choice among the available corrosion protection techniques due to their effectiveness in terms of functionality and cost. The use of traditional and toxic corrosion inhibitors has led to environmental issues, arousing the need for green counterparts that are environmentally friendly, easily accessible, biodegradable, and cost-effective. In this review, the utilization of green corrosion inhibitors purely acquired from renewable sources is explored, with an in-depth focus on the recent advancements in the use of fruit and vegetable extracts as green corrosion inhibitors. In particular, fruits and vegetables are natural sources of various phytochemicals that exhibit key potential in corrosion inhibition. To shed light on the true potential of such extracts in the protection of steel in acidic environments, the experimental techniques involved in corrosion inhibition and the mechanism of corrosion inhibition are discussed in detail. The study highlights the potential of fruit and vegetable extracts as non-toxic, economical, and effective corrosion inhibitors in the pursuit of green chemistry. In addition to discussing and outlining the current status and opportunities for employing fruit and vegetable extracts as corrosion inhibitors, the current review outlines the challenges involved in the utilization of such extracts in corrosion inhibition.

Development of a novel multiepitope chimeric vaccine against anthrax.

Bacillus anthracis (BA), the etiological agent of anthrax, secretes protective antigen (PA), lethal factor (LF), and edema factor (EF) as major virulence mediators. Amongst these, PA-based vaccines are most effective for providing immunity against BA, but their low shelf life limits their usage. Previous studies showed that B-cell epitopes, ID II and ID III present in PA domain IV possess higher toxin neutralization activity and elicit higher antibody titer than ID I. Moreover, N-terminal region of both LF and EF harbors PA-binding sites which share 100% identity with each other. Here, in this study, we have developed an epitope-based chimeric vaccine (ID-LFn) comprising ID II-ID III region of PA and N-terminal region of LF. We have also evaluated its protective efficacy as well as stability and found it to be more stable than PA-based vaccine. Binding reactivities of ID-LFn with anti-PA/LF/EF antibodies were determined by ELISA. The stability of chimeric vaccine was assessed using circular dichroism spectroscopy. ID-LFn response was characterized by toxin neutralization, lymphocyte proliferation isotyping and cytokine profiling. The protective efficacy was analyzed by challenging ID-LFn-immunized mice with B. anthracis (pXO1+ and pXO2+). ID-LFn was found to be significantly stable as compared to PA. Anti-ID-LFn antibodies recognized PA, LF as well as EF. The T-cell response and the protective efficacy of ID-LFn were found to be almost similar to PA. ID-LFn exhibits equal protective efficacy in mice and possesses more stability as compared to PA along with the capability of recognizing PA, LF and EF at the same time. Thus, it can be considered as an improved vaccine against anthrax with better shelf life. ID-LFn, a novel multiepitope chimeric anthrax vaccine: ID-LFn comprises of immunodominant epitopes of domain 4 of PA and N-terminal homologous stretch of LF and EF. The administration of this protein as a vaccine provides protection against anthrax.

Characterization of a two component system, Bas1213-1214, important for oxidative stress in Bacillus anthracis.

Microbial colonization is an outcome of appropriate sensing and regulation of its gene expression. Bacillus anthracis adapts and thrives in its environment through complex regulatory mechanisms, among them, the two component systems (TCS). Many bacteria respond to the oxygen fluctuations via TCS. In the present work, a previously uncharacterized TCS, Bas1213-1214, of B. anthracis with a probable role in oxygen sensing has been characterized as a functional TCS. A substantial increase in the expression of Bas1213 was observed during the stationary growth phase, in presence of bicarbonate ions, and under oxidative stress thereby speculating the role of Bas1213 in toxin production and adaptive responses. Electrophoretic mobility shift assay (EMSA) and ANS assay highlighted autoregulation of the system. Identification of Bas1213 regulon further suggested its regulatory function in metabolism and adaptive responses. A marked reduction in sporulation was observed on overexpression of Bas1213 in B. anthracis which can be correlated with the augmented expression of sporulation kinase D. Additionally, Bas1213 was shown to regulate catalase, and ABC transporter (mntH) further implicating its essential role during oxidative stress. Finally, crucial residues involved in the DNA binding activity of Bas1213 were also identified. This study reports that the role of Bas1213-1214 in the regulation of metabolism and adaptive responses during oxidative stress. Both sporulation and response to environmental oxygen are important for the maintenance of B. anthracis lifecycle, therefore, characterization of Bas1213-1214 provides a step closer toward understanding the regulatory network governing in B. anthracis.

A Sir2 family protein Rv1151c deacetylates HU to alter its DNA binding mode in Mycobacterium tuberculosis.

Till recently, knowledge about epigenetic regulation in bacterial world confined largely to DNA methylation. Lysine acetylation/deacetylation of histones is a major contributor for chromatin dynamics in eukaryotes. However, little is known about such epigenetic changes brought about by post-translational modifications in bacteria. Here, we describe an example of such mechanism occurring in a histone like protein, HU from Mycobacterium tuberculosis (Mtb). Previously, we demonstrated the interaction and acetylation of Mtb HU (MtHU) by one of the acetyl transferases, Eis. In this work, we demonstrate the deacetylation of acetylated HU (MtHUAc) by Rv1151c, the only Sir2 like protein discovered in Mtb. The DNA binding properties of MtHU are significantly altered upon acetylation but reversed consequent to deacetylation by the deacetylase. Deacetylated HU (MtHUdAc) bound to relaxed DNA leading to the formation of looped and dense molecules as compared to open structures formed by its acetylated form. Interaction of MtHUdAc with linear DNA modifies its organization leading to formation of highly bridged compact structures while binding of MtHUAc leads to the formation of stiff and straight rods. That a nucleoid associated protein can undergo acetylation/deacetylation to alter its DNA binding and architectural role opens up a new dimension of investigation of epigenetic regulation in mycobacteria.

The conserved hypothetical protein Rv0574c is required for cell wall integrity, stress tolerance, and virulence of Mycobacterium tuberculosis.

The virulence of Mycobacterium tuberculosis is intimately related to its distinctive cell wall. The biological significance of poly-α-L-glutamine (PLG), a component in the cell wall of virulent mycobacteria, has not been explored adequately. The focus of this study is to investigate the role of a locus, Rv0574c, coding for a polyglutamate synthase-like protein, in the synthesis of poly-α-L-glutamine in the context of mycobacterial virulence. Evaluation of Rv0574c gene expression in M. tuberculosis demonstrated its growth-phase-linked induction with concomitant accumulation of poly-α-L-glutamine in the cell wall. Rv0574c was activated under conditions prevalent in the tubercular granuloma, e.g., hypoxia, nitric oxide, and CO2. For functional characterization, we produced a deletion mutant of the Rv0574c gene by allelic exchange. The mutant produced smaller amounts of poly-α-L-glutamine in the cell wall than did the wild-type bacterium. Additionally, the increased sensitivity of the mutant to antitubercular drugs, SDS, lysozyme, and mechanical stress was accompanied by a drastic reduction in the ability to form biofilm. Growth of the ΔRv0574c strain was normal under in vitro conditions but was retarded in THP-1 macrophages and in the lungs and spleen of BALB/c mice. This was in agreement with histopathology of the lungs showing slow growth and less severe pathology than that of the wild-type strain. In summary, this study demonstrates that the protein encoded by the Rv0574c locus, by virtue of modulating PLG content in the cell wall, helps in maintaining cellular integrity in a hostile host environment. Also, its involvement in protecting the pathogen from host-generated lethal factors contributes to the infectious biology of M. tuberculosis.

Low expression level of glnA1 accounts for absence of cell wall associated poly-l-glutamate/glutamine in Mycobacterium smegmatis.

Cell wall associated poly-l-glutamine (PLG) layer synthesis is directly linked to glutamine synthetase (GS) encoded by glnA1 in tuberculosis causing mycobacteria. Avirulent Mycobacterium smegmatis (M. smegmatis) despite of having a glnA1 homolog lacks cell wall associated PLG layer. In the present study, we complemented a ΔglnA1 mutant of Mycobacterium bovis (lack PLG in cell wall) with M. smegmatis glnA1 cloned under M. bovis glnA1 promoter. PLG synthesis was restored in the cell wall of complemented strain. The complemented strain also showed increased resistance to physical stresses such as lysozyme, SDS and increased survival in THP-1 macrophages in comparison to the knockout. Further, in ß-galactosidase reporter assay M. smegmatis glnA1 promoter showed ten times less activity as compared to M. bovis glnA1 promoter. GACT-8-11 → TGAC mutations in the M. smegmatis glnA1 promoter restored its activity by 60% as compared to the activity of glnA1 promoter of M. bovis. This mutation also showed increased GS expression and produced cell wall associated PLG in M. smegmatis. The results of this study demonstrate that glnA1 promoter of M. smegmatis accounts for low expression level of GS and apparently responsible for absence of cell wall associated PLG layer.

Unveiling the orchestration: mycobacterial small RNAs as key mediators in host-pathogen interactions.

Small RNA (sRNA) molecules, a class of non-coding RNAs, have emerged as pivotal players in the regulation of gene expression and cellular processes. Mycobacterium tuberculosis and other pathogenic mycobacteria produce diverse small RNA species that modulate bacterial physiology and pathogenesis. Recent advances in RNA sequencing have enabled identification of novel small RNAs and characterization of their regulatory functions. This review discusses the multifaceted roles of bacterial small RNAs, covering their biogenesis, classification, and functional diversity. Small RNAs (sRNAs) play pivotal roles in orchestrating diverse cellular processes, ranging from gene silencing to epigenetic modifications, across a broad spectrum of organisms. While traditionally associated with eukaryotic systems, recent research has unveiled their presence and significance within bacterial domains as well. Unlike their eukaryotic counterparts, which primarily function within the context of RNA interference (RNAi) pathways, bacterial sRNAs predominantly act through base-pairing interactions with target mRNAs, leading to post-transcriptional regulation. This fundamental distinction underscores the necessity of elucidating the unique roles and regulatory mechanisms of bacterial sRNAs in bacterial adaptation and survival. By doing these myriad functions, they regulate bacterial growth, metabolism, virulence, and drug resistance. In Mycobacterium tuberculosis, apart from having various roles in the bacillus itself, small RNA molecules have emerged as key regulators of gene expression and mediators of host-pathogen interactions. Understanding sRNA regulatory networks in mycobacteria can drive our understanding of significant role they play in regulating virulence and adaptation to the host environment. Detailed functional characterization of Mtb sRNAs at the host-pathogen interface is required to fully elucidate the complex sRNA-mediated gene regulatory networks deployed by Mtb, to manipulate the host. A deeper understanding of this aspect could pave the development of novel diagnostic and therapeutic strategies for tuberculosis.

Core to concept: synthesis, structure, and reactivity of nanoscale zero-valent iron (NZVI) for wastewater remediation.

Numerous technological advancements have been developed to tackle the issue of wastewater remediation effectively. However, the practical application of these technologies on a large scale has faced several challenges that have hindered their progress. These challenges include low selectivity, high energy requirements, and significant expenses. Nanoscale materials have demonstrated remarkable effectiveness in removing a wide range of contaminants. Nanoscale zero-valent iron (NZVI) exhibits a range of distinctive physical and chemical properties that have proven to be highly effective in various environmental remediation applications. These include its impressive surface area, remarkable reactivity, and its capacity to create stable colloidal suspensions. The paper explores the synthetic techniques for NZVI with special emphasis on green synthesis and the use of capping or support agents for maintaining stability and enhancing the reactivity of NZVI. The various structural and reactivity aspects of NZVI have been highlighted for its potential application in wastewater treatment sequestrating various categories of inorganic and organic contaminants. The discussion also delves into the limitations of NZVI, highlighting its dependence on water as a medium for contact reaction or electron transfer through the action mechanism of NZVI in adsorptive and photocatalytic sequestration of contaminants. The beneficial potential of NZVI-based composite systems in the field of environmental remediation has also been included which aids in the application of NZVI in environmental remediation.

COVID-19 pandemic - Cocktail of variants, a study from Northern India.

Context: The aim of the study was to identify and monitor the circulating strains of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the samples received at our center and update the existing national and international genomic surveillance data. Introduction: SARS-CoV-2 is no exception to the basic nature of the viruses ability to change and evolve. Since its first report in December 2019 from Wuhan, China, multiple variants of the virus have emerged and been reported. Five variants of concern have been recognized and reported by the Centers for Disease Control and Prevention, which are associated with variable degrees of transmissibility and mortality. Materials and Methods: Nasopharyngeal and oropharyngeal swabs received in viral transport medium at the Viral Research Diagnostic Laboratory were processed for reverse transcription-polymerase chain reaction for SARS-CoV-2. Whole genome sequencing (WGS) was performed for selective positive samples using Oxford Nanopore sequencing technology, using MinKNOW software for data acquisition. Statistical Analysis: The clades were assigned using Nextclade v2.4.1 software. The statistical analysis was calculated using OpenEpi version 3, an open-source calculator, and two by two. Results: Variants reported over the study period included Alpha, Kappa, Delta, and Omicron. Delta dominated in the year 2021, while Omicron was the dominant variant in 2022. In both the dominant variants, asymptomatics contributed to around 30-40% of positives. Intensive care unit admissions and mortality were higher in the Delta variant, while vaccination history and travel history were higher in the patients with Omicron variant. Conclusion: The trend tracking of these variants has been important in view of public health, enabling early interventions to control the spread of the disease and foresight in preparation for the situation.

Enhanced Zn(II) adsorption by chemically modified sawdust based biosorbents.

Heavy metals present in industrial effluents, when discharged into water channels, not only affect humans but also negatively impact plants and aquatic organisms. Sawdust is available readily in developing countries and can be used by small-scale industries for effluent water treatment containing low concentrations of bivalent zinc ions. This study explores the potential of sawdust-derived biosorbents, after boiling (SDB), chemical modification with formaldehyde (SDF), and sulfuric acid (SDS), for sequestration of Zn(II) from simulated wastewater as well as industrial effluents. The morphological analysis of the three biosorbents indicated a suitable porous structure with a pore size of 232.928 m2/g (SDB), 291.102 m2/g (SDF), and 498.873 m2/g (SDS). The functional analysis of native and metal-laden biosorbents indicated the role of - OH, - C = O, and - NH functional groups in Zn(II) binding. The process parameters were optimized and the spontaneous adsorption of Zn(II) was found to proceed by multilayer formation by following pseudo-second-order kinetics. SDS adsorbent (0.1 g) exhibited a greater potential for removal of Zn(II) from industrial effluents as compared to SDB and SDF at pH = 6.0 with the equilibrium adsorption capacity of 45.87 mg/g. Therefore, SDS could be a promising adsorbent for the treatment of wastewater in small-scale industries.

Utilization of biosynthesized silica-supported iron oxide nanocomposites for the adsorptive removal of heavy metal ions from aqueous solutions.

This study deals with heavy metal ions removal from simulated water using biosynthesized silica-supported iron oxide nanocomposites (nano-IOS). Agricultural and garden wastes have been utilized to prepare nano-IOS through a green synthesis process. Nano-IOS was characterized by XRD, SEM, FTIR, and zeta potential analysis. The nanocomposites were used to remove five heavy metals, viz., Pb2+, Cd2+, Ni2+, Cu2+, and Zn2+, with optimization of reaction parameters including pH, the concentration of heavy metals, adsorbent dosage, and contact time in batch mode experiments. The optimized dose of nano-IOS was 0.75 g/L for the adsorption of Pb2+, Cd2+, Ni2+, Cu2+, and Zn2+ (10.0 mg/L) with a contact duration of 70 min at pH 5.0 for Pb2+, Cd2+, and Cu2+ and 6.0 for Ni2+ and Zn2+. The adsorption behavior of the nano-adsorbent was well described by Langmuir adsorption isotherm and pseudo-second-order kinetic model indicating chemisorption on the surface of nano-IOS. The adsorption was also found spontaneous and endothermic. Thus, the environmentally benign and bio-synthesized nano-IOS can be utilized as an effective nano-adsorbent for the rapid sequestration of heavy metal ions from water and wastewater.

Rapid adsorptive removal of chromium from wastewater using walnut-derived biosorbents.

Contamination of water resources by industrial effluents containing heavy metal ions and management of solid waste from agricultural and food industries is a serious issue. This study presents the valorization of waste walnut shells as an effective and environment-friendly biosorbent for sequestrating Cr(VI) from aqueous media. The native walnut shell powder (NWP) was chemically modified with alkali (AWP) and citric acid (CWP) to obtain modified biosorbents with abundant availability of pores as active centers, as confirmed by BET analysis. During batch adsorption studies, the process parameters for Cr(VI) adsorption were optimized at pH 2.0. The adsorption data were fitted to isotherm and kinetic models to compute various adsorption parameters. The adsorption pattern of Cr(VI) was well explained by the Langmuir model suggesting the adsorbate monolayer formation on the surface of the biosorbents. The maximum adsorption capacity, qm, for Cr(VI) was achieved for CWP (75.26 mg/g), followed by AWP (69.56 mg/g) and NWP (64.82 mg/g). Treatment with sodium hydroxide and citric acid improved the adsorption efficiency of the biosorbent by 4.5 and 8.2%, respectively. The endothermic and spontaneous adsorption was observed to trail the pseudo-second-order kinetics under optimized process parameters. Thus, the chemically modified walnut shell powder can be an eco-friendly adsorbent for Cr(VI) from aqueous solutions.

Theoretical and experimental studies on photocatalytic removal of methylene blue (MetB) from aqueous solution using oyster shell synthesized CaO nanoparticles (CaONP-O).

The development of technologies for the removal of dye from aqueous solution is most desirable if the end product is relatively green (i.e., environmentally friendly). Photodegradation (as one of such technology) and photolysis (without the catalyst) was applied to investigate the role of sol-gel synthesized calcium oxide nanoparticle (using the oyster shell as the precursor). The results obtained gave substantial evidence that calcium oxide nanoparticles catalyzed the degradation of the methylene blue dye up to a maximum percentage of 98 % removal. Degradation efficiency displayed a strong dependency on time, initial dye concentration, catalyst load, pH, and ionic strength. Chi-square and sum of square error analysis indicated that the photodegradation kinetics fitted the Langmuir-Hinshelwood, first order, and pseudo first-order models best. The half-life of the dye was significantly reduced from hours to minutes due to photocatalysis. Quantum chemical calculations indicated that the degradation proceeded through adsorption, deformation/degradation, and desorption through the chloride end of the molecule linked to the calcium active center of the catalyst. Results from Fukui functions and molecular descriptors analysis confirmed the mechanism of photocatalysis.

Quantum and experimental investigation of the application of Crassostrea gasar (mangrove oyster) shell-based CaO nanoparticles as adsorbent and photocatalyst for the removal of procaine penicillin from aqueous solution.

The present study was designed to synthesize and characterize calcium oxide nanoparticles (using mangrove oyster shell as a precursor) and apply the synthesized nanoparticles as a photocatalyst to degrade procaine penicillin in an aqueous solution. The photocatalyst exhibited an average band gap of 4.42 eV, showed a maximum wavelength of absorbance in the UV region (i.e., 280 nm), and is a microporous nanoparticle with a particle diameter of 50 nm. The photocatalyzed degradation of the drug was conducted under natural sunlight, and the influence of parameters such as the period of contact, catalyst load, pH, initial drug concentration, and ionic strength was investigated concerning the degradation profile. The results obtained from response surface analysis indicated that an optimum degradation efficiency of about 93% can be obtained at a concentration, pH, and catalyst dosage of 0.125 M, 2, and 0.20 g respectively, at 0.902 desirabilities. The Langmuir-Hinshelwood, modified Freundlich, parabolic diffusion, pseudo-first-/second-order, and zero-, first-, and second-order kinetic parameters were tested to ascertain the best model that best described the experimental data. Consequently, the Langmuir-Hinshelwood, modified Freundlich, and pseudo-second-order models were accepted based on the minimum error and higher R2 values. Based on the Langmuir-Hinshelwood rate constants for adsorption and photodegradation as well as the evaluated valence bond potential, the degradation of the drug first proceeded through the mechanism of adsorption and followed by the oxidation of the drug by superoxide (generated from the interaction of electrons that generated by through the absorption of UV radiation). The quantum chemical calculation gave evidence that pointed towards the establishment of strong agreement with experimental data and also showed that the carboxyl functional group in the drug is the target site for adsorption and subsequent degradation.