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, q_m, 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.

Microbial induced calcite precipitation (MICP) is a part and consequence of metabolic activities of many bacterial species with involvement of various pathways in presence of specific organic and/or inorganic moieties present in the surrounding environment. Microbial or Bioconcrete is a sustainable and promising technology based on MICP that not only supports the self-healing of concrete structures but also mitigates the detrimental effects of CO₂ emissions on environment from the cement industry. The calcite precipitation inside concrete matrix results in crack healing with an improvement in matrix characteristics. This paper reviews the various mechanisms involved in MICP and highlights the role of MICP in self-healing inside cement matrix. The paper further throws light on designing of microbial concrete and explores the beneficiary effects of MICP on various mechanical and durability properties of cementitious materials. Further, the prospective challenges associated with microbial concrete production and the future aspects have been discussed.

Nanoparticles (NPs) have become an important field of research over the past several decades with applications in various sectors, such as biomedical, cosmetic, food and many others, because of their unique characteristics. The green synthesis of nanoparticles has been preferred because of the naturally occurring reductants present in biological systems that decreases exposure to toxic chemicals compared with physico -chemical methods and is eco-friendly. Zinc oxide (ZnO) NPs exhibit broad and potential applications in different fields with their specific characteristics such as surface area, size, shape, low toxicity, optical properties, high binding energy and large band gap. This paper focuses on the bio-synthesis of ZnO NPs by utilizing extracts of different plant parts (stem, flower, fruit, peel, and leaves) through efficient, economical, simple, pure, and eco-friendly green routes. In this process, zinc salts have been used as precursor and phytochemicals in the plant extract reduce the metal salt to lower oxidation state as well as stabilize the ZnO NPs. The morphological and physico-chemical properties of obtained NPs analyzed by various characterization techniques have been discoursed. Further, antimicrobial activity and potential photocatalytic application in terms of the degradation of dyes have also been reviewed in addition to the toxicity aspects of these NPs on human beings and animals.

Post-harvest loss of agriproducts is a major issue of concern not only for the farmers but also for the distributors, sellers, and consumers as it significantly affects the economic aspects associated with the large-scale agriproduct industry. This loss is mainly due to the attack of various pathogens, and contact with various chemicals or gases present in the atmosphere such as oxygen, carbon dioxide, water, etc. leading to a loss of visual appeal, nutritional content, and quality along with a reduction in the shelf life of products. The use of nanotechnology has provided innovative solutions to this problem with the application of nanomaterials such as nanoparticles, nanocomposites, and nano-films in coating, packaging, and diagnostics. This paper highlights the role of nanotechnology to enhance the shelf life, visual appeal, and nutritional value of agriproducts by protecting them from the harmful environment and other agents. In this regard, the in-vivo and in-vitro studies conducted for the antimicrobial potential of nanoparticles have been explored for various pathogens. The use of nano-coatings and nanosensors in active packaging has been discussed. Biodegradable packaging, the need of the hour in the context of environmental issues has also been explored.

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.