Chikmagalur Raju Girish

Bentonite material was prepared and examined for the adsorptive removal of Cr (VI) from an aqueous solution. The bentonite was characterized by XRD, FTIR, SEM-EDS, BET and DLS analyses. The experimental design optimization results for the adsorption (AN) of Cr (VI) onto the bentonite adsorbent (AB) determined using the Central Composite Design were pH: 4, adsorbent dose (AD): 1.0 g/100mL, initial Cr (VI) concentration (ICC): 200 mg/L, and contact time (CT): 60 min for a maximum Cr (VI) removal of 86.92%. The Cr (VI) AN onto bentonite fitted to Langmuir isotherm and an AN capacity of 25.17 mg/g was obtained. The kinetics of the process showed Elovich model and the AB also exhibited good reusability over various cycles. Various machine learning methods such as Linear Regression (LR), random forest regressor (RFR), Support Vector Regression (SVR), Gradient Boosting (GB), Artificial Neural Networks (ANNs) were investigated. Among these, the GB and SVR come out as the best model achieved R ² (0.987, and 0.995) the lowest MAE (0.194, and 0.210) and RMSE (0.359 and 0.371), which predicts the AN value very close to the experimental results. This integration of machine learning and environmental chemistry provides a powerful tool for developing cost-effective and sustainable water treatment systems using naturally available materials.

The discharge of pharmaceutical active compounds (PhACs) into aquatic environments has become a growing concern due to their adverse effects on both aquatic organisms and human health. Simultaneously, the global spread of invasive weeds disrupts ecosystems, leading to significant environmental and economic consequences. This study investigates competitive adsorption of acetaminophen (ACT) and tetracycline (TET) using green-synthesized ZnO-biochar derived from Prosopis juliflora (ZPJC). ZPJC was characterized using SEM, EDX, FTIR, XRD, TGA, and pH_pzc analyses and applied in both batch and column experiments for monocomponent (ACT/TET) and multicomponent (ACT+TET) systems. Batch experiments examined the impact of operational parameters such as initial PhAC concentration (0.1–10 mg/L), contact time (1–180 min), pH (3–11), and ZPJC dose (0.25–4 g/L). Column experiments explored the variations in bed depth (3–9 cm), flow rate (0.5–2 L/h), and influent concentration (1–5 mg/L). Optimal conditions (60 min, 6.5 pH, and 3 g/L ZPJC dose) resulted in a maximum adsorption capacity of 5.27 mg/g for TET and 9.26 mg/g for ACT in the batch system, following pseudo-second-order and Langmuir models, suggesting chemisorption dominance. For column systems, the Thomas and Yoon–Nelson models better represented experimental data. Adsorption efficiency improved with increasing bed depth and flow rate, while it declined with higher PhAC concentration. In multicomponent batch systems, TET exhibited antagonistic effects due to site competition and steric effects, whereas ACT demonstrated slight synergism. However, in column systems, both ACT and TET displayed antagonistic interactions. Scale-up design of the column elucidates that ZPJC can be adopted as a sustainable solution for the removal of PhACs while addressing invasive weed proliferation.

The quality evaluation of the activated carbon made from agricultural waste is investigated in the adsorption of phenol. Adsorbent was prepared through the activation of orthophosphoric acid, producing a structure that is porous with a surface area of 1090 m²/g. Elemental composition analysis confirmed that the carbon composition is 78.23%. X-ray photoelectron spectroscopy (XPS) and other characterizations were conducted to study the structural, chemical and thermal performance metrics. The results from the Boehm titration were aligned with the point of zero charge. Response Surface Methodology was used to optimize adsorption parameters. The adsorption outcomes demonstrated the effectiveness of phenolic removal, with the Langmuir isotherm under optimal conditions exhibiting a maximum adsorption capacity of 185.93 mg/g. The study on the kinetics of adsorption showed that they closely matched the second-order pseudo model (R² > 0.98). Thermodynamic studies indicate that adsorption occurs spontaneously, as evidenced by negative ΔG° values. This further validates its exothermic nature and decreases randomness at the solid–liquid interface, as indicated by negative ΔH° and ΔS° values. The adsorbent regeneration and spiking studies were methodically examined. Activation energy and isosteric heat of adsorption were assessed. The adsorption mechanism is discussed thoroughly. These results highlight the effectiveness of activated carbon as a practical adsorbent for treating wastewater.

Numerous contaminants are released into the environment by industrial effluent. The pollutants have harmful effect on the environment and are required to be treated. Adsorption using activated carbon is one of the promising methods for removing the pollutants. Thermodynamic studies in adsorption play a significant role as it determines energy requirement and feasibility of the process. The significance of thermodynamic parameters, such as activation energy, isosteric heat of adsorption, DR model constants, enthalpy, Gibbs free energy and entropy, is studied. Its significance in the adsorption, its role in deciding the type of mechanism and nature of the process are reviewed in this paper.

Industrial effluent is a complex aqueous matrix comprising hazardous substances like phenols and toxic organics, often mixed with nutrients, suspended solids and multiple pollutants. Its constituents vary with industry, making it a significant environmental challenge requiring targeted treatment solutions. So, in the present research, competitive adsorption of phenol and 2,4-Dichlorophenol (2,4-DCP) onto Cassia fistula-derived activated carbon (CFPAC) was investigated. In case of phenol adsorption, the modified Langmuir isotherm was found to appropriately align with experimental data and achieving R² greater than 0.95 and least Marquardt's percent standard deviation (MPSD), although certain overestimation was observed in the predicted values. Similarly, in case of 2,4-DCP, the experimental values closely aligned with both modified Langmuir and modified Redlich–Peterson isotherm as reflected by higher R²; however, the estimated values were underestimated. For both pollutants, the adsorption ratio (Rq_i) was less than one. Further, the P-factor (P_fi) was exceeding 1 along with positive ΔIE_i implies an antagonistic type of interaction between phenol and 2,4-DCP. The binary desorption of pollutant was effective across for four adsorption–desorption cycles demonstrating the consistent performance of CFPAC. Graphical Abstract

Herein, Casuarina equisetifolia-derived activated carbon was developed by pyrolysis at a low temperature (773 K). The derived adsorbent was characterized as an extremely porous and amorphous carbon with a surface area of 1007 m²/g. The point of zero charge (pH_PZC) of activated carbon was obtained as 3.89. The reported carbon was used for the remediation of phenolic pollutants [phenol and 2,4-dichlorophenol (2,4-DCP)]. To begin with, the optimization of parameters demonstrated that a pH of 2 and a temperature of 293 K had significant impacts on the adsorption of both pollutants. The isotherm studies revealed that the Freundlich (R ² = 0.9956) and Langmuir (R ² = 0.9866) models better fitted the adsorption of phenol and 2,4-DCP, respectively. The study also reported an exceptionally elevated monolayer adsorption efficiency of 364.62 and 382.03 mg/g for phenol and 2,4-DCP, respectively. This significantly greater adsorption would aid in the elimination of phenolic pollutants, especially in coal processing industries, which are major contributors to phenolic discharge. Furthermore, kinetic studies revealed that the chemisorption mechanism dominated with R ² > 0.999 for all concentrations ranging between 25 and 200 mg/L. In addition, the thermodynamic behavior of phenol and 2,4-DCP revealed exothermic (ΔH < -26.70 kJ/mol) and feasible type of adsorption. The value of isosteric heat of adsorption corroborated physisorption dominating the entire process with ΔH _x < 25 kJ/mol. The adsorption mechanism aspect of phenol/2,4-DCP suggests that the removal of pollutants followed a combination of physical and chemical adsorption, accompanied by pore diffusion and electrostatic attraction coupled with π-π interaction and hydrogen bonding. The Casuarina equisetifolia activated carbon (CEAC) performed significantly well for four cycles of adsorption-desorption. The broader significance of these findings would yield sustainable production of Casuarina equisetifolia-derived carbon, which is an easily available carbon-rich source, additionally offering a cost-effective alternative solution/replacement for the remediation of phenol and chlorinated phenols from synthetic wastewater.

The progress of industrial and agricultural pursuits, along with the release of inadequately treated effluents especially phenolic pollutant, has amplified the pollution load on environment. These organic compounds pose considerable challenges in both drinking water and wastewater systems, given their toxicity, demanding high oxygen and limited biodegradability. Thus, developing an eco-friendly, low-cost and highly efficient adsorbent to treat the organic pollutants has become an important task. The present investigation highlights development of a novel adsorbent (CFPAC) by activation of Cassia fistula pod shell for the purpose of removing phenol and 2,4-dichlorophnenol (2,4-DCP). The significant operational factors (dosage, pH, concentration, temperature, speed) were also investigated. The factors such as pH = 2 and T = 20°C were found to be significant at 1.6 g/L and 0.6 g/L dosage for phenol and 2,4-DCP respectively. Batch experiments were further conducted to study isotherms, kinetic and thermodynamics studies for the removal of phenol and 2,4-DCP. The activated carbon was characterised as mesoporous (specific surface area 1146 m²/g, pore volume = 0.8628 cc/g), amorphous and pH_PZC = 6.4. At optimum conditions, the maximum sorption capacity for phenol and 2,4-DCP were 183.79 mg/g and 374.4 mg/g respectively. The adsorption isotherm was better conformed to Redlich Peterson isotherm (phenol) and Langmuir isotherm (2,4-DCP). The kinetic study obeyed pseudo-second-order type behaviour for both the pollutants with R² > 0.999. The thermodynamic studies and the value of isosteric heat of adsorption for both the pollutants suggested that the adsorption reaction was dominated by physical adsorption (ΔH_x < 80 kJ/mol). Further, the whole process was feasible, exothermic and spontaneous in nature. The overall studies suggested that the activated carbon synthesised from Cassia fistula pods can be a promising adsorbent for phenolic compounds. Graphical Abstract