Biological synthesis of GO-MgO nanomaterial using Azadirachta indica leaf extract: A potential bio-adsorbent for removing Cr(VI) ions from aqueous media

Adsorption and catalytic reduction of hexavalent chromium based on nanomaterials: A review on metal, metallic oxide, metallic sulfide and carbon-based catalyst

Chromium (Cr) is widely recognized as a significant environmental contaminant and a major contributor to global pollution. As a result, there is a strong emphasis on developing effective methods for the removal and reduction of Cr(VI). This review examines various applications of nanomaterial catalysts, including metallic oxides, metals, metallic sulfides, and carbon-based materials. These materials encompass naturally occurring substances, synthetically produced compounds, and artificially modified forms, all of which typically exhibit favorable adsorption properties and catalytic activity. We systematically summarize the mechanisms of adsorption and catalytic reduction associated with these nanomaterials, including photocatalysis, electrocatalysis, and direct catalysis. Finally, we explore the future directions and prospects of nanomaterials in environmental remediation, highlighting the key challenges that must be addressed in this field.

New Schiff base covalently bonded graphene oxide for removing chromium(VI) from surface runoff

Hexavalent chromium (Cr(VI)) poses severe health and environmental risk, especially in industrial vicinities where runoff concentrations are elevated by evaporation and sedimentation dynamics. This study investigates the utilization of modified graphene oxide (GO) with abundant active groups as an adsorbent. The novel adsorbent, GO/ATA, was synthesized by covalently attaching a Schiff base (ATA) to GO via a coupling reaction, enhancing its adsorptive properties. The physicochemical properties of GO/ATA were meticulously characterized to ascertain structural and morphological attributes. GO/ATA exhibit exceptional adsorptive capabilities, surpassing the performance parameters of other adsorbents with a maximum of 243.3 mg g-1 at 298 K. The electrostatic attraction between the N-containing functional groups in the graphene oxide and Schiff base composite (GO/ATA) and Cr(VI) is the main mechanism behind the adsorption process; Subsequently, a reduction reaction occurs, facilitated by the thiol and N-containing functional groups in GO/ATA composite, resulting in the transformation of Cr(VI) into Cr(III). This transformation is essential for the following chelation process occurring on the surface of the adsorbent material. Evaluations of recyclability indicated that GO/ATA retains substantial adsorption efficacy, with a reduction from 91.2% to 72.7% over five cycles, thus affirming its recyclability and practical application in the remediation of Cr(VI)-contaminated waterborne environment. Additionally, GO/ATA's effectiveness in removing Cr(VI) from surface runoff was specifically tested, emphasizing its economic and environmental viability.

A Review of Different Synthesis Approaches to Nanoparticles: Bibliometric Profile

Nanomaterials are currently one of the most popular emerging materials used in different applications such as drug delivery, water treatment, cancer treatment, electronic, food preservations, and production of pesticide. This is due to their interesting features including size-dependent properties, lightweight, biocompatibility, amphiphilicity and biodegradability. They offer wide possibilities for modification and are used in multiple functions with enormous possibilities. Some of them are medically suitable which has opened new opportunities for medical improvement especially for human health. These characteristics also make nanomaterials one of the pioneers in green materials for various needs, especially in environmental engineering and energy sectors. In this review, several synthesis approaches for nanoparticles mainly physical, chemical, and biological have been discussed extensively. Furthermore, bibliometric analysis on the synthesis of nanoparticles was evaluated. About 117,162 publications were considered, of which 92% are journal publications. RSC Advances is the most published outlet on the synthesis of nanoparticles and China has the highest number of researchers engaged in the synthesis of nanoparticles. It was noted in the evaluation of synthesis approach that biological approach is the savest method but with a low yield, while the chemical approach offers a high yield with some level of hazardous effect. Also, the bibliometric analysis revealed that the field of nanotechnology is a trending and hot ground for research.

Development of innovative and green adsorbents for in situ cleanup of fluoride-polluted groundwater: Mechanisms and field-scale studies

In this study, the magnesium oxide (MgO)-based adsorbents [granulated MgO aggregates (GA-MgO) and surface-modified MgO powder (SM-MgO)] were developed to remediate a fluoride-contaminated groundwater site. Both GA-MgO and SM-MgO had porous, spherical, and crystalline structures. Diameters for GA-MgO and SM-MgO were 1-1.7 mm and 1-10 μm, respectively. The pseudo second-order dynamic adsorption and the Freundlich isotherm could be applied to express the chemical adsorption phenomena. The monolayer adsorption was the dominant mechanism at the initial adsorption period. During the latter part of fluoride adsorption, the multilayer adsorption became the dominant mechanism for fluoride removal from the water phase, which also resulted in the increased adsorption capacity. Higher hydroxide, phosphate, and carbonate concentrations caused a decreased fluoride removal efficiency due to the competition of sorption sites between fluoride and other anions with similar electronic properties. Fluoride removal mechanism using GA-MgO and SM-MgO as the adsorbents was mainly carried out by the chemical adsorption. Reaction paths contained two main processes: (1) formation of magnesium hydroxide after the reaction of MgO with water, and (2) the hydroxyl group of the magnesium hydroxide was replaced by fluoride ions to form magnesium fluoride precipitation. Results from column tests show that up to 61 and 73% of fluoride removal (initial fluoride concentration = 9.3 mg/L) could be obtained after 50 pore volumes of groundwater pumping with GA-MgO and SM-MgO injection, respectively. The GA-MgO system could be applied to contain and remediate fluoride-contaminated groundwater, and SM-MgO could be applied as an immediate fluoride removal alternative to achieve a rapid pollutant removal for emergency responses. Up to 71% of fluoride removal (fluoride concentration = 10.8 mg/L) could be obtained with GA-MgO injection after 30 days of operation. The developed GA-MgO system is a potential and green remediation alternative to contain the fluoride plume significantly.

Adsorption of hexavalent chromium using Water Hyacinth Leaf Protein Concentrate/Graphene Oxide hydrogel

Water Hyacinth Leaf Protein Concentrate/Graphene Oxide (WHLPC/GO) hydrogel was synthesized for the removal of Cr(VI) from wastewater. About 90% of the prepared hydrogel constitutes WHLPC. The prepared material was characterized by FT-IR and XRD. The process variables such as pH, contact time, adsorbent dosage, initial Cr(VI) concentration, and temperature were optimized using a batch mode experiment. Kinetic studies were also conducted and it was observed that the chemosorptive pseudo-second-order best described the adsorption system with a correlation coefficient (R2) of 0.984. The highest adsorption capacity of 322.00 mg/g was achieved at pH 1.0, and equilibrium was achieved within 420 min. Various isotherm models were analyzed using non-linear fitting. It was found that the Sips model provides the best fit, indicating heterogeneous and uniform active site surface adsorption of Cr(VI) on the WHLPC/GO. The reuse efficiency of the synthesized material was also found to be greater than 84% for five consecutive cycles. Thermodynamic studies were conducted and results revealed that the adsorption was spontaneous and endothermic.

A critical review on the bio-mediated green synthesis and multiple applications of magnesium oxide nanoparticles

Nowadays, advancements in nanotechnology have efficiently solved many global problems, such as environmental pollution, climate change, and infectious diseases. Nano-scaled materials have played a central role in this evolution. Chemical synthesis of nanomaterials, however, required hazardous chemicals, unsafe, eco-unfriendly, and cost-ineffective, calling for green synthesis methods. Here, we review the green synthesis of MgO nanoparticles and their applications in biochemical, environmental remediation, catalysis, and energy production. Green MgO nanoparticles can be safely produced using biomolecules extracted from plants, fungus, bacteria, algae, and lichens. They exhibited fascinating and unique properties in morphology, surface area, particle size, and stabilization. Green MgO nanoparticles served as excellent antimicrobial agents, adsorbents, colorimetric sensors, and had enormous potential in biomedical therapies against cancers, oxidants, diseases, and the sensing detection of dopamine. In addition, green MgO nanoparticles are of great interests in plant pathogens, phytoremediation, plant cell and organ culture, and seed germination in the agricultural sector. This review also highlighted recent advances in using green MgO nanoparticles as nanocatalysts, nano-fertilizers, and nano-pesticides. Thanks to many emerging applications, green MgO nanoparticles can become a promising platform for future studies.

Microbased biorefinery for gold nanoparticle production: recent advancements, applications and future aspects

Multifaceted utility of nanomaterials is indispensable to meet the environmental challenges across the globe. Nanomaterials substantially contribute in delineating the rapidly advancing field of nanotechnology. Recently, primary emphasis has been laid down on augmenting the biological methodologies for the synthesis of nanomaterials. In this aspect, green nanotechnology has revolutionized the entire process of nanosynthesis. Essentially biofabrication of nanoparticles have long-range applications, primarily in the field of medical applications such as drug delivery, cancer diagnostics and genetic engineering processes. Biocompatible and stable nanoparticles synthesized from biological source can be an effective approach against the chemically synthesized owing to their non-expensive and eco-friendly attributes. Biological systems including bacteria, yeasts, fungi and plants have already been exploited in the field of nanotechnology. Use of fungi seems to be a very effective and economical approach for the synthesis of gold nanoparticles. Gold nanoparticles possess anti-oxidation activity, are highly stable and biocompatible in nature. Fungi-mediated nanoparticle biosynthesis is more advantageous as compared to bacterial synthesis. Fungi secrete large amounts of enzymes, whereas the enzyme secretion of yeasts is weak. Here, we have reported the recent advancements and future implications in the field of gold nanoparticle production and applications.