Amarendra Dhar Dwivedi

Protocol for development of various plants leaves extract in single-pot synthesis of metal nanoparticles

This article is aimed to extend a simple protocol for preparation of various plant leaves extract and their application to green synthesis of the metallic nanoparticles. Five plant leaves extract showed mild reduction and stabilization ability for silver and gold nanoparticles (AgNPs and AuNPs) at room temperature. The particle size range varied from 25 to 42 nm and 21 to 47 nm for AgNPs and AuNPs, respectively. Plant leaves extract-mediated nanoparticles were characterized to confirm the shape, size, crystallinity, and content using different spectroscopic investigations. Differences in stability of nanoparticles at different pH were also measured by zeta potential.

Biocatalytic Synthesis Pathways, Transformation, and Toxicity of Nanoparticles in the Environment

Wide application of nanoparticles (NPs) in consumer products over the last decade has increased their flux in the environment. This paper provides comprehensive review on the biocatalytic production pathways, transformations, and toxicity to human and other organisms of important NPs. Plants, algae, fungi, and bacteria have been used for energy-efficient and nontoxic biocatalytic production of NPs. The process is simple, serving as an alternative to the more popular physicochemical methods. NPs go through significant physicochemical transformation in the environment. Ionic strength, pH, and NPs’ surface potential strongly influence their stability and aggregation. Their transformations are linked to their bioavailability and aging including surface coatings and dissolved organic carbon effects. In addition, nanotoxicity has been a major global concern as NPs are toxic to organisms due to their cytotoxicity and genotoxicity. The stability and transformation of NPs in environment influence their short- and long-term toxicity. Release of free metal ions, dissolution-enhanced toxicity, and direct intercalation with biological targets are studied the most. Their toxicity to ecological receptors and organisms are linked to oxidative stress by generation of reactive oxygen species. Moreover, NPs toxicity depends on their physicochemical alterations. Inherent and acquired properties have potential to alter toxicity of NPs. Thus achieving safe nanotechnology and minimizing their adverse impact is important to protect the health of humans as well as the environment.

Single-step green synthesis of imine-functionalized carbon spheres and their application in uranium removal from aqueous solution

Carbon spheres (CSs) have become a recent focus of attention in environmental remediation techniques. In this study, imine-functionalized CSs were synthesized from plant extract (peCSs) for the first time and effectively used in U(VI) removal from contaminated water. Plant extracts of Sorbaria sorbifolia were utilized for the synthesis of peCSs via a single-step hydrothermal carbonization, and the physico-chemical properties of the synthesized peCSs were characterized by spectroscopic analysis. The peCSs showed high nitrogen content (∼7.49%) due to the presence of naturally occurring cyanogenic glycosides and mesoporosity (8.31 nm). The plant extract concentration played an important role in determining the size of the peCSs, which ranged from 0.5 to 3.0 μm. The adsorption capacity (Qm) of peCSs for U(VI) (Qm ≈ 113 mg g−1) was higher than that of the glucose-derived CSs (Qm ≈ 57 mg g−1) and commercial powdered activated carbon (Qm ≈ 44 mg g−1). A plausible mechanism for the higher adsorption efficacy of peCSs was proposed via sorbate–sorbent interactions. The ionic strength (0.01 M to 1 M NaCl) showed the weakest effect on the U(VI) adsorption. The multiple adsorption–desorption cycling test revealed that the efficacy of peCSs does not significantly decrease after repetitive use.

Distinctive green recovery of silver species from modified cellulose: Mechanism and spectroscopic studies

The present study aimed to recover precious silver in order to identify the adsorption coupled reduction pathways that determine this process. A combination technique of adsorption and nanocrystallization was used to investigate the recovery of silver species from taurine-cellulose (T-DAC) samples. The non-synthetic route of nanocrystallization yielded spherical zero-valent silver sized ∼ 18 nm. Rate-controlling steps were modeled by adsorption parameters by the best fit of Langmuir capacity (55 mg/g), pseudo-second order curves, and exothermic chemical reactions. The T-DAC was an excellent sorbing phase for the treatment of silver-polluted waters over a broad range of pH (2.1-10.1) and varying ionic strengths (8.5-850 mM, as NaCl), which are the conditions often encountered in industrial and mining effluents. A good recovery of silver (40-65%) was also obtained in the presence of Cd(II), Co(II), Cr(VI), Ni(II), and As(V) at lower or equivalent concentrations with Ag(I), either from individually added metals or from all metal ions mixed together. Desorption was compared with a series of five eluents including complexing agents. In these experiments acidified thiourea yielded 86% desorption of Ag(I). Aqueous silver reduced to metallic silver on the surface of the T-DAC samples, which was confirmed by X-ray photo electron spectroscopy.

Process Design of Groundnut Husk Waste for Pb2+ and Cd2+ Ions Mitigation in Drinking Water Purification

This present work has explored a novel application of modified Arachis hypogaea (groundnut) husk on mitigation of toxic Pb2+ and Cd2+ ions in aqueous phase. Ecotoxicological assessment of exhausted adsorbent was investigated as per standard OECD guidelines. Standard deviation, correlation coefficient, and the reduced chi square test were evaluated and compared statistically on experimental data. The results showed good sorption capacities—31.62 and 29.78 mg g−l for Pb2+ and Cd2+ ions, respectively. Pseudo first-order rate kinetics was well correlated for Pb2+ and Cd2+ ions sorption over all kinetic models. The sorption data was in good agreement with the Freundlich isotherm for Pb2+ and the Sips model for Cd2+ ions sorption. The sorption capacity was endothermic in nature. Pb2+ ions desorption was three times faster than Cd2+ ions. The sorption mechanism was plausibly explained by spectroscopic techniques. Herein, the tailored abundant agro-waste material is a competitive sorbent and may be exploited in decontamination of metal ions in a wide range of concentrations. Supplemental materials are available for this article. Go to the publishers online edition of Separation Science and Technology to view the free supplemental file.