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Aquaculture wastewater containing tetracycline hydrochloride (TCH) poses significant environmental problems and health risks. We investigated the adsorption of TCH onto phosphoric acid-activated corncob biochar (PCC) as a sustainable and efficient removal strategy. PCC was synthesized from cob feedstock activated by phosphoric acid under a pyrolysis temperature of 300 °C in a limited-air atmosphere. It was characterized extensively, revealing a high specific surface area (1071.75 m /g), high porosity with total pore volume of 0.912 cm /g, and abundant surface functional groups including phosphate, carboxylic, and amine groups. Batch adsorption experiments demonstrated an ultrahigh adsorption capacity for TCH, with a maximum theoretical capacity (Langmuir model) of 953.62 mg/g at 313 K. Its adsorption isotherms transfer from Langmuir type to Freundlich type as temperature rises, indicating a transition from monolayer to multilayer adsorption. The adsorption kinetics were governed by a synergistic mechanism involving surface adsorption and a pore-filling effect (intra-particle diffusion). Critically, the adsorption dynamics exhibit an intra-particle diffusion-controlled process at a low pH (3.0) during the final stage of adsorption. Strong hydrogen bonding led to high initial adsorption rates, and the adsorption converted to diffusion-controlled mode eventually. In contrast, at higher pH (≥7.0), electrostatic repulsion between PCC adsorbents and TCH molecules hindered intra-particle diffusion, causing the final adsorption stage to deviate from diffusion control. This work provides comprehensive insights into the pH-dependent interfacial interactions and kinetics governing TCH removal by corncob-derived, phosphoric acid-activated biochar.

This study investigates the removal of Congo red dye from aqueous solution using functionalized generation 3.0 and 5.0 Polyamidoamine dendrimer – silica gel composite (G-3PS, G-5PS). Fourier Transform-Infra Red spectroscopy, Brunauer Emmett and Teller, Thermogravimetric Analysis, pH at point of zero charge, and Scanning Electron Microscopy measurements have been applied to characterize the synthetic nanohybride composite, these techniques revealed the successful functionalization of both dendrimer molecules and subsequent immobilization onto silica gel. The implications of varying adsorption parameters such as contact time, initial concentration of adsorbate, temperature and pH on both composites were studied. Experimental data obtained from batch adsorption processes were fitted into two equilibrium isotherms (Langmuir and Freundlich) and 3 kinetic models (Pseudo-First-Order, Pseudo-Second-Order, Intra Particle Diffusion). Adsorption mechanism was mainly governed by film diffusion due to electrostatic interactions between the functionalized dendrimer surface and Congo red molecules. Thermodynamic parameters illustrate that the adsorption is endothermic and spontaneous. Findings suggest the Nanocomposites G-3PS G-5PS) are good adsorbents for the removal of Congo red dye from aqueous solutions.

Adsorption processes are widely used in different technological areas and industry sectors, thus continuously attracting attention in the scientific research and publications. Design and scale-up of these processes are essentially based on the knowledge and understanding of the adsorption kinetics and mechanism. Adsorption kinetics is usually modeled by using several well-known models including the pseudo-first and pseudo-second order models, the Elovich equation, and the intra-particle diffusion based models. However, in the scientific literature there are a significant number of cases with the inappropriate use of these models, utilization of erroneous expressions, and incorrect interpretation of the obtained results. This paper is especially focused on applications of the pseudo-second order, intra-particle diffusion and the Weber-Morris models, which are illustrated with typical examples. Finally, general recommendations for selection of the appropriate kinetic model and model assumptions, data regression analysis, and evaluation and presentation of the obtained results are outlined.

Among various environmental pollutants, dyes have been reported to contaminate a large quantity of surface water. Rhodamine B, a widely applicable basic dye, is known for its hazardous impact on environment. The present study proposes the application of readily available waste banana peels for the remediation of water contaminated with Rhodamine B. The potential of prepared material to decontaminate Rhodamine B was examined as the function of various parameters. Variation in adsorption time, dose of adsorbent, pH value, and initial concentration has been observed under the influence of diverse condition. Quantitative adsorption was observed at a contact time of 60 min with an adsorbent dose of 12 mg. An increase in the initial dye concentration resulted in the enhancement of adsorption capacity of adsorbent. The value of enthalpy change was observed to be − 8.95 kJ mol−1. The negative value indicates the exothermic removal of Rhodamine B from water. Various models were applied to explain thermodynamics and kinetics of the process. Adsorption kinetics was better explained with pseudo-second-order model, whereas adsorption mechanism by intra-particle diffusion model reveals that pore diffusion was not only the rate-controlling step.

Pesticide transport in the environment is impacted by the kinetics of its adsorption onto soil. The adsorption kinetics of pyrimethanil was investigated in ten soil samples of varying physicochemical properties. The highest adsorption was in the soil having the maximum silt and CaCO3 contents, pH and electrical conductance but the lowest amorphous Fe oxides and CaCl2 extractable Mn. Pseudo-second order kinetics and intra-particle diffusion model best accounted the adsorption kinetics of pyrimethanil. The equilibrium adsorption estimated by pseudo-second order kinetics (q02) was significantly and positively correlated with CaCl2 extractable Cu content (r = 0.709) while rate coefficient (k02) had a negative correlation with crystalline iron oxides content (r = -0.675). The intra-particle diffusion coefficient (ki.d.) had inverse relationship with CaCl2 extractable Mn content in soils (r = -0.689). FTIR spectra showed a significant interaction of pyrimethanil with micronutrient cations. Adsorption kinetic parameters of pyrimethanil could be successfully predicted by soil properties. The findings may help to evolve fungicide management decisions.

The aim of this study was to prepare activated carbon from tobacco stalks using microwave heating. The prepared activated carbon was applied as an adsorbent in methylene blue (MB) removal from water. The optimum conditions for activated carbon preparation were a radiation power of 280 W for a period of 6 minutes after the impregnation of the precursor material with 30% ZnCl2 for 24 hours. The activated carbon yield and iodine number were 49.43% and 1,264.51 mg/g respectively. The activated carbon also had a point of zero charge of 5.81 with an adsorption capacity of 123.45 mg/g for MB. The optimum conditions for MB adsorption were a pH of 6.5 with an adsorbent dosage of 0.2 g/50 mL at 25 °C. The MB adsorption kinetics followed the pseudo second order kinetic model with the intra-particle diffusion model suggesting a two-step adsorption mechanism. The adsorption data also fitted well within the Langmuir adsorption isotherm model. Tobacco stalks can successfully be turned into an economically important product.

Nanocellulose from jute fiber was grafted with sodium itaconate through esterification with itaconic anhydride followed by replacement of surface protons with sodium ions. A tea-bag pouch containing sodium itaconate grafted nanocellulose (SINC) acted as a chemisorbant for lead ions through ion exchange when dipped in an aqueous solution. Surface morphology and surface modification of SINC were characterized by FTIR, SEM, EDX, TEM, AFM and BET N2 adsorption isotherm techniques. The effective diminution of lead ion concentration was ascertained by AAS and ICP-MS methods. The impact of operating parameters like residence time, temperature, ion concentration and pH on the chemisorption capability was evaluated. The kinetic data conformed to the intra particle diffusion model and pseudo second order reaction. The Freundlich model was found to be the best for describing isotherm equilibrium. The maximum chemisorption capacity (mg g−1) of SINC, nanocellulose itaconate and nanocellulose in aqueous solution for Pb2+ were found to be 85, 58 and 10 respectively at pH 5.5. The used SINC was easily regenerated via desorption of lead ion using NaCl. The regenerated SINC could be reused for four consecutive cycles with no loss of chemisorption efficiency. The SINC was also effective for removal of other metal ions such as chromium, cadmium and mercury. This is an easily synthesizable, adaptable and well-chemisorbing system with proven reusability. This could emerge as an economical alternative to the conventional cation exchange resins.Graphic abstractItaconic acid functionalization of nanocellulose resulted in a cation exchange resin with good chemisorption capability, regenerability and reusability in solution.

The present study investigated the use of pretreated fish bone (PTFB) as a new surface, natural waste and low-cost adsorbent for the adsorption of Methyl green (MG, as model toxic basic dye) from aqueous solutions. The functional groups and surface morphology of the untreated fish bone (FB) and pretreated fish bone were characterized using Fourier transform infrared (FTIR), scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS), respectively. The effect of operating parameters including contact time, pH, adsorbent dose, temperature, and inorganic salt was evaluated. Langmuir, Freundlich and Temkin adsorption isotherm models were studied and the results showed that the adsorption of basic dye followed Freundlich isotherm. Kinetic modeling of the data at different temperatures confirmed pseudo-second-order(P-2-O) model, along with calculated thermodynamic parameters depicted that the adsorption process is spontaneous and endothermic in nature. Diffusion studies suggested that intra-particle diffusion is not the singular rate-controlling factor. The results indicated that 92% of MG capable of being sequestered under optimum adsorption conditions: pH 10.64, adsorbent dose 0.1 g/L, and 60 min contact time. Finally, the results showed that the pretreated fish bone can be effectively used as a proper adsorbent for the adsorption of cationic dye from aqueous solutions.

In the present study, a series of hypercrosslinked resins (CH series) was prepared in systematically designed conditions for the adsorption of nitroaromatics from aqueous solution. The newly synthesized CH-10 possesses a Brunauer–Emmett–Teller (BET) surface area up to 1,329.3 m2/g which is larger than that of the widely used hypercrosslinked resin H-103 and it exhibits great advantage over H-103 when subjected to nitrobenzene at low concentrations. The adsorption capacity of CH-10 for nitrobenzene is 1.4 times as much as that of H-103 at the concentration of 100 mg/L. Kinetic study by film diffusion model and intra-particle diffusion model revealed that its distinctive mesoporous structure within pore diameters between 2 and 6 nm played significant role in the mass transfer at low concentrations, and these unique mesopores also resulted in better adsorption capacity, which was confirmed by adsorption thermodynamics study. Moreover, the CH series displayed a good affinity to a wide scope of nitroaromatics and exhibited excellent dynamic adsorption and desorption properties in fixed bed.

This study reports the sustainable valorization of chicken bone waste into high-performance activated carbon (CBAC) for the removal of malathion, an organophosphorus pesticide, from aqueous systems. CBAC was synthesized via KOH activation at 800 °C, yielding a microporous material with a BET surface area of 1,125 m²/g and total pore volume of 0.92 cm³/g. FTIR, SEM, and BET analyses confirmed the presence of abundant oxygen-containing functional groups and a highly developed pore structure. Adsorption experiments revealed a maximum capacity of 84.03 mg/g for malathion at an initial concentration of 40 mg/L, with an optimal pH of 6.0 achieving 96.4% removal efficiency. Batch adsorption studies revealed optimal performance at pH 6, with an equilibrium adsorption capacity of 142.8 mg/g, fitting well to the Langmuir isotherm (R² = 0.992) and pseudo-second-order kinetics (R² = 0.987). The intra-particle diffusion model indicated a multi-stage adsorption mechanism involving surface interaction and pore diffusion. Comparative tests demonstrated CBAC’s superior efficiency over commercial activated carbon. The adsorption process was thermodynamically spontaneous and endothermic. A preliminary cost estimation suggested that CBAC production from waste chicken bones is economically feasible, supporting its potential for large-scale application. This work demonstrates a circular bioeconomy approach to waste valorization while offering an effective and low-cost adsorbent for pesticide remediation.