Volume 35, Issue 7

Biochar (BC) generated from thermal and hydrothermal cracking of biomass is a carbon-rich product with the microporous structure. The graphene-like structure of BC contains different chemical functional groups (e.g. phenolic, carboxylic, carbonylic, etc.), making it a very attractive tool for wastewater treatment, CO 2 capture, toxic gas adsorption, soil amendment, supercapacitors, catalytic applications, etc. However, the carbonaceous and mineral structure of BC has a potential to accept more favorable functional groups and discard undesirable groups through different chemical processes. The current review aims at providing a comprehensive overview on different chemical modification mechanisms and exploring their effects on BC physicochemical properties, functionalities, and applications. To reach these objectives, the processes of oxidation (using either acidic or alkaline oxidizing agents), amination, sulfonation, metal oxide impregnation, and magnetization are investigated and compared. The nature of precursor materials, modification preparatory/conditions, and post-modification processes as the key factors which influence the final product properties are considered in detail; however, the focus is dedicated to the most common methods and those with technological importance.

In recent years, membrane distillation (MD) has evidently emerged as one of the promising separation processes, with increasing areas of application including but not limited to desalination, pharmaceutical and textile wastewater purification, food processing, concentration of aqueous solution, breaking azeotropic mixtures, and extraction of volatile organic compounds. Primarily, MD has been categorized on the basis of vapor collection and condensation arrangement methods. Among the various categories, air gap membrane distillation (AGMD), in which an air gap is maintained across the membrane and the cooling plate, turns out to be an important and efficient process. Lately, AGMD has received significant attention of researchers around the world which motivates the present work. This paper aims to review the work done so far concerning the AGMD in order to provide a holistic view that covers the principles and applications of AGMD, effect of process parameters, membrane parameters, mathematical modeling, fouling, temperature and concentration polarization, types of membrane module, energy consumption, recent developments in AGMD process, cost estimation, and heat integration with AGMD. To the best of our knowledge, the present work is the first attempt to exhaustively review the AGMD process.

Nanoparticles have high potential as antibacterial agents, owing to their ability to produce reactive oxygen species (ROS). Recent studies have indicated that this ROS generation is highly affected by the modification of band structure by the introduction of various dopant materials into them. Thus, doped nanoparticles have been extensively studied in the recent literature. The types of dopants, synthesis techniques, and experimental parameters have been found to affect the overall electronic structure of the material, leading to varied antibacterial efficiency. This review summarizes some of the prominent dopant nanomaterials, various methods of synthesizing doped nanoparticles used against bacterial cells, and the main factors involved in it. Despite the extensive research on the mechanism of the antibacterial action, it is still poorly understood mainly due to the inherent complexities and dynamics in cell membranes. Some of the major proposed mechanisms of action of each kind of dopant nanomaterial have also been reported in this work, focusing on the bacterial cell structure.