Parametric Studies on Descriptive Isotherms for the Uptake of Crystal Violet Dye from Aqueous Solution onto Lignin-Rich Adsorbent

Deep analysis of adsorption isotherm for rapid sorption of Acid Blue 93 and Reactive Red 195 on reactive graphene

Graphene-based adsorbent was prepared by adopting a green synthetic route via the chemical exfoliation of graphite and low-temperature thermal activation. Prepared reactive graphene (RG) was characterized through various techniques, and its adsorption capabilities for textile dye removal were investigated for Acid Blue-93 (AB) and Reactive Red-195 (RR) under different operational conditions. The dye sorption equilibrium and mechanism were comprehensively studied using isotherm and kinetic models and compared statistically to explain the sorption behavior. Results show AB and RR adsorption by RG attains equilibrium in 60 min and 70 min, with a high sorption quantity of 397 mg g-1 and 262 mg g-1 (initial dye concentration of 100 mg L-1), respectively. The dye sorption anticipates that the high surface area (104.52 m2 gm-1) and constructed meso-macroporous features of RG facilitated the interaction between the dye molecules and graphitic skeleton. The R-P isotherm fitted the best of equilibrium data, having the least variance in residuals for both dyes (AB = 0.00031 and RR = 0.00047). The pseudo-second order model best fitted the kinetics of sorption on RG, with chemisorption being the predominant process delimiting step. The overall results promise the dye removal capability of RG to be an efficient adsorbent for azo-based dyes from textile effluents.

Lignin/PVA hydrogel with enhanced structural stability for cationic dye removal

In this study, a lignin-based hydrogel for wastewater treatment was prepared by incorporating kraft lignin (KL) into a poly (vinyl alcohol) (PVA) matrix. The underwater structural stability of the KL-PVA hydrogel was guaranteed through physicochemical crosslinking, involving freeze-thaw process and chemical crosslinking reaction. The KL-PVA hydrogel displayed superior compressive characteristics compared to the original PVA hydrogel. This improvement was attributed to the chemical crosslinking and the reinforcing effect of the incorporated KL microparticles. The incorporation of anionic KL microparticles into the PVA three-dimensional network structure enhanced the cationic methylene blue (MB) and crystal violet (CV) adsorption efficiency of the prepared KL-PVA hydrogel. The MB adsorption results were well explained by pseudo-2nd order kinetics model and Langmuir isotherm model. Electrostatic forces, hydrogen bonding and π-π stacking interactions were the main adsorption mechanisms between cationic dyes and KL surfaces, indicating the potential of KL-PVA hydrogel as an effective adsorption material. Moreover, regulating the molecular weight of PVA not only prevented lignin leakage from the KL-PVA hydrogel but also elevated the KL content within the hydrogel, consequently improving its dye removal performance. For KL-PVA hydrogel with high molecular weight PVA, the MB and CV adsorption capacities were 193.8 mg/g and 190.0 mg/g, respectively.

Cellulose and its derivatives, coffee grounds, and cross-linked, β-cyclodextrin in the race for the highest sorption capacity of cationic dyes in accordance with the principles of sustainable development

In this study, seven different materials were analyzed and includes coffee grounds (CG), two types of cellulose (CGC and CC), two types of modified cellulose (CT and CTCD), and cross-linked β-cyclodextrin (CD-1 and CD-2) were tested as adsorbents for the removal of dyes from the wastewater. The composition, morphology, and presence of functional groups in the obtained sorption materials were characterized by elemental analysis, SEM, TG/DTA, and FTIR spectroscopy. The sorption processes of the model contaminant, crystal violet (CV), were studied by kinetics and equilibrium models. The results showed, that using CTCD, the dye was adsorbed rapidly in 1 min and the slowest adsorption occurred in 20 min by CG. The time evolution was adjusted using a two-model, pseudo second-order model (CG and CGC) and pseudo first-order model in the rest adsorbents. According to the Langmuir and Sips isotherm models, the maximum adsorption capacities were very high in each case ranging from 1092.24 to 1220.40 mg g^-1. Moreover, the adsorption capacity of the near-natural materials remained even higher after five regeneration cycles. The regeneration is almost waste-free and the materials used can be decomposed during composting. In addition, almost complete removal of cationic dyes was observed during the treatment of real wastewater samples.

Removal of ibuprofen from aqueous media by adsorption: A comprehensive review

Ibuprofen (IBP) is a non-steroidal anti-inflammatory drug released into the environment through hospital and medical effluents, pharmaceutical wastewater and veterinary use. The aim of this paper is to review the empirical findings on the adsorption of IBP from aqueous media. A preliminary ecotoxicological assessment confirmed the environmental risk of IBP in the aqueous environment. Open literature works considered in this review were for the past decade (2010-2020). Carbon-based adsorbents are the best class of adsorbent for the uptake of IBP and the highest reported maximum adsorption capacity (q_max) for IBP is 496.1 mg/g by SWCNTs. The range of adsorption capacities for IBP uptake in this review is between 0.0496 and 496.1 mg/g. The mechanism of uptake is majorly by hydrophobic interactions, π - π stacking, hydrogen bonds, electrostatic interactions and dipole-dipole interaction. IBP uptake was best fit to a wide variety of isotherm models but was well suited to the pseudo-second order kinetics model. The thermodynamics of IBP uptake depends majorly on the nature of the adsorbent and desorption from the solid phase is based on an appropriate choice of the eluent. Knowledge gaps were observed in used adsorbent disposal and process improvement. In the future, interest would increase in scale-up, industrial applications and practical utilisation of the research findings which would help in sustainable water resource management.

Efficacy of treated sodium alginate and activated carbon fibre for Pb(II) adsorption

Efficacy of treated sodium alginate (TSA) and activated carbon fibre (ACF) for aqueous Pb(II) uptake was comparatively investigated. By employing FTIR, SEM, EDX, XRD, point of zero charges and surface area measurements, the available functional groups, morphology, crystallinity, surface charge and surface areas of both adsorbents were respectively elucidated. The Pb(II) uptake performance of both adsorbents was also studied via batch mode at varied process conditions. The experimental isotherm and kinetic data for both adsorbents were best fitted to nonlinear forms of Langmuir and pseudo-first-order models, respectively. Similarly, intraparticle diffusion was the sole controlling mechanism. Despite the huge variation in the surface area, TSA (7.8 m²/g) with high carboxyl content (395.6 meq-COOH/100 g of sample) performed better by all standards than the ACF (975 m²/g). This finding showed that although the surface area of a given adsorbent is a key indicator of its adsorptive performance, the inherent surface functional groups play a superior role. The experimentally derived maximum adsorption capacities of 221.25 mg/g (for TSA) and 183.34 mg/g (for ACF) were recorded at an equilibrium time of 30 min and 45 min, respectively. Therefore, TSA and ACF demonstrated effectiveness for aqueous Pb (II) sequestration.

Agricultural waste

The management of agricultural waste has become very important because the inappropriate disposal yields negative effects on the environment. The resource recovery from agricultural waste which converts waste into available resources can reduce the waste and new resource consumption. This review summarizes the 2018 researches of over three hundred scholar papers from several aspects: agricultural waste, and, waste chemical characterization, agricultural waste material, adsorption, waste energy, composting, waste biogas, agricultural waste management, and others.