Effective Cd2+ removal from water using novel micro-mesoporous activated carbons obtained from tobacco: CCD approach, optimization, kinetic, and isotherm studies

Recent progress on tobacco wastes-derived adsorbents for the remediation of aquatic pollutants: A review

Tobacco (Nicotiana tabacum L.) is a significant crop widely planted worldwide. Its leaves have a special economical value as raw materials for the cigarette industry. During tobacco harvesting and cigarette production, a large amount of wastes that could not be used in the cigarette industry are generated such as tobacco stems, stalks, and low-grade leaves. The utilization of such agro-industrial wastes in raw or carbonaceous form as adsorbents for wastewater treatment is an economic and eco-friendly step for elimination of such waste. Tobacco waste can be directly applied as adsorbents for aquatic pollutants owing to its favorable lignocellulosic composition and functional groups enriched structure. Moreover, this waste has high volatile matters and thus can be an efficient precursor for high surface area carbonaceous adsorbents including biochar and activated carbon with high removal performance. This article is a recent and comprehensive review about the preparation of adsorbents (raw, biochar and activated carbon) from different tobacco wastes (stems, stalks, leaves, etc.) along with its characterization and regeneration. The adsorption behavior of different aquatic adsorbates on these adsorbents under specific conditions along with the isotherm, kinetic, thermodynamic, and mechanism studies is also considered. The highest uptakes for most tested pollutants were 399.0, 195.2, and 173.0 mg/g for lead, chromium, and cadmium, 517.5 mg/g for methylene blue, and 210.66 and 1.602 mg/g for phosphate and chlorpyrifos. Significant findings and future ideas for the studied adsorbate/adsorbent systems are finally given.

Chemical Modification of Teff Straw Biomass for Adsorptive Removal of Cr (VI) from Aqueous Solution: Characterization, Optimization, Kinetics, and Thermodynamic Aspects

Teff straw, a by-product of Teff, mainly available in Ethiopia, has not been studied much for biosorbent production. The present study has investigated the effects of modification and optimization of process parameters (viz., concentration of modifying agent (H3PO4 and KOH), modifying temperature, and modifying time) on the Cr (VI) removal efficiency of using chemically activated Teff straw biosorbent by RSM followed by BBD. The maximum Cr (VI) removal was obtained using an H3PO4-modified Teff straw biosorbent of 92.5% with 2 M concentration of the modifying agent, 110°C, and 4 h. Similarly, maximum Cr (VI) removal using KOH-modified Teff straw biosorbent of 95.2% was obtained with 1.5 M activating agent concentration, 105°C activation temperature, and 3.5 h activation time. In addition, the effects of adsorption parameters (viz., biosorbent dosage, temperature, initial concentration of Cr (VI), and contact time) were investigated. The maximum removal efficiency was attained at 2 g of biosorbent dosage, 4 h contact, 75 mg/L of initial Cr (VI) concentration, and 25°C sorption temperature. In addition, isotherm, kinetic, and thermodynamic studies for Cr (VI) biosorption were studied. The experimental adsorption data were well fitted with the Langmuir isotherm and pseudo-second-order kinetic model with higher correlation coefficient in both untreated and chemically modified Teff straw biosorbent. The investigated thermodynamic parameters ( $\Delta H^o$ , $\Delta S^o$ , and $\Delta G^o$ ) confirmed that Cr (VI) metal ions’ adsorption process onto Teff straw biosorbent was spontaneous and endothermic.