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A nano-biosorbent for the removal of methylene blue (MB) was prepared by encapsulating iron oxide nanoparticles (NPs) and Agrobacterium fabrum strain SLAJ731, in calcium alginate. The prepared biosorbent was optimized for the maximum adsorption capacity at pH 11, 160 rpm, and 25 °C. Adsorption kinetics was examined using pseudo-first-order, pseudo-second-order, and intra-particle diffusion (IPD) models. The kinetic data agreed to pseudo-second-order model indicating chemisorption of MB, which was also explained by FTIR analysis. The adsorption rate constant ( k 2 ) decreased and initial adsorption rate (h, mg g −1 min −1 ) increased, with an increase in initial dye concentration. The dye adsorption process included both IPD and surface adsorption, where IPD was found to be a rate-limiting step after 60 min of adsorption. The adsorption capacity was found to be 91 mg g −1 at 200 mg L −1 dye concentration. Adsorption data fitted well to Freundlich isotherm; however, it did not fit to Langmuir isotherm, indicating adsorbent surfaces were not completely saturated (monolayer formed) up to the concentration of 200 mg L −1 of MB. Thermodynamic studies proposed that the adsorption process was spontaneous and exothermic in nature. Biosorbent showed no significant decrease in adsorption capacity even after four consecutive cycles. The present study demonstrated dead biomass along with NPs as a potential biosorbent for the treatment of toxic industrial effluents.

In the present study, Juglans regia shells were used to prepare activated carbon by acid treatment method. J. regia shell-based activated carbon was used for the adsorption of two synthetic dyes namely, a basic dye malachite green and an acid dye amido black 10B. The prepared adsorbent was crushed and sieved to three different mesh sizes 100, 600 and 1,000 μm. The adsorbent was characterized by scanning electron microscopy, surface acidity and zero-point charge. Batch experiments were carried out by varying the parameters like initial aqueous phase pH, adsorbent dosage and initial dye concentration. The equilibrium data were tested with Langmuir, Freundlich, Redlich-Peterson and Sips isotherm at three different temperatures 293, 300 and 313 K and it was found that the Freundlich isotherm best fitted the adsorption of both the dyes. Kinetic data were tested with pseudo first-order model and pseudo second-order model. The mechanism for the adsorption of both the dyes onto the adsorbent was studied by fitting the kinetic data with intraparticle diffusion model and Boyd plot. External mass transfer was found to be the rate-determining step. Based on the ionic nature of the adsorbates, the extent of film diffusion and intraparticle diffusion varied; both being system specific. Thermodynamic parameters were also calculated. Finally, the process parameters of each adsorption system were compared to develop the understanding of the best suitable system.

Cotton gin trash (CGT), a residual lignocellulosic biomass generated during the ginning process of cotton fibres, is proposed for valorization and application in environmental remediation. Taking advantage of its availability and composition, rich in hydroxyl, carboxyl, and carbonyl groups, CGT is studied for its suitability for dye removal. Cotton gin trash films are synthesized using a single-step process with formic acid and tested for methylene blue (MB) adsorption. The morphology, chemical structure, surface area, zeta potential and crystallinity of the films are also reported. The hydroxyl groups in CGT increased by the film preparation and further enhanced the zeta potential of CGT towards the negative direction. Overall, the adsorption process is governed by the physisorption characteristic, where a greater potential difference between CGT and cationic MB improved the dye uptake. The adsorption system is described as favourable, fitting better with Langmuir isotherm model. The maximum adsorption capacity of the CGT films is 209 mg/g, which compares favourably against other reported lignocellulosic materials. Overall, the results indicate the CGT has an enormous potential as an adsorbent material for dye separation from wastewaters.Graphic abstract

Dye wastewater containing non-fixed dyes discarded from different manufacturing industries is a major concern in environmental pollution. Amongst all other non-fixed dyes, anionic dyes hold a significant share in the dye wastewater (32–90%) stream, due to their extensive uses. In this study, cotton gin trash (CGT) is proposed for valorisation and utilisation as a bioadsorbent for the anionic dye. Gin trash was transformed into a film by a single-step process. Since −OH group rich CGT film tends to adsorb cationic dye, chitosan that has adsorption capability towards anionic dyes was used to modify CGT by introducing positive charges for the adsorption of anionic Acid Blue 25 (AB). The morphology, roughness, chemical structure and zeta potential of the raw CGT powder and chitosan-modified CGT (CHT–CGT) film were reported. The fabricated film showed roughness and pores in the surface favouring the dye adsorption. The adsorption process followed the physisorption phenomenon rather than the chemisorption process, where cationic CHT–CGT film attracted anionic AB. Kinetics and equilibrium adsorption of the system were described as favourable, fitting better with the Langmuir model compared to Freundlich, Dubinin–Radushkevich and Flory–Huggins isotherms. The maximum adsorption of the CHT–CGT film was 151.5 mg/g, compares favourably among other reported lignocellulosic waste. Besides, CHT–CGT film was found reusable after desorption, without significantly altering its removal efficiency. The results along with our previous report explore a sustainable pathway of adding value to CGT as a dye bioadsorbent from wastewater, where unmodified and chitosan-modified CGT films together have the potential to separate both cationic and anionic dyes concurrently.Graphic abstract

PurposeWith the developments of new materials and technologies for adsorption, it is necessary to develop new kinetic models to describe some more complex adsorption processes. This study aimed to evaluate the availability of a modified intraparticle diffusion model qt = k1t1/2 (0 ≤ t ≤ t1) and qt-qt=t1 = k2 (t-t1)1/2 (t1 < t ≤ t2) for the adsorption of chlorobenzene pollutants (CBs) on biochar and to explore the corresponding mechanisms.Materials and methodsThe adsorption kinetics of the four CBs with different numbers of Cl substituents were investigated in mono- or multi-CB adsorption experiments (equal or unequal initial concentration) with the corn straw-based biochar pyrolyzed at 500 °C. The kinetics process was fitted by the classical model (qt = kt1/2 + b) with linearization or nonlinearly regression, and by the modified intraparticle diffusion model qt = kt1/2 (0 ≤ t ≤ t1) and qt-qt=t1 = k2 (t-t1)1/2 (t1 < t ≤ t2). The optimal break point of t1 separating the stages of 0 ≤ t ≤ t1 and t1 < t ≤ t2 was obtained by comparing the parameters of adjR2 and AICc calculated from different t1 values. Combined with the characteristics of biochar morphology and structure, variation of initial concentrations and performances of competitive adsorption of CBs, the adsorption mechanisms were analyzed.Results and discussionThe modified model performed well the nonlinear fitting of the kinetic processes with R2 values between 0.917 and 0.981, higher than that of the nonlinear and linear fitting of the classical model. The adsorption rate of k1 was usually larger than k2 regardless of the number of chlorine substitutions, or in the scenario of mono-/multi-CBs adsorption. In the mono-adsorption, the k1 and k2 values of low-chlorinated CBs were mostly greater than those of the high-chlorinated CBs. In multi-adsorption, competitive adsorption decreased the intraparticle diffusion rates of each CBs. And the rates varied with the initial concentration of CBs, and with the numbers of chlorine substitutions which had an effect on the affinities of CBs to biochar and steric hindrance via hydrophobicity, electrophilicity and molecule sizes.ConclusionsThe modified intraparticle diffusion model was suggested to be suitable to describe the diffusion processes of CBs with high aqueous phase concentrations on biochar. The modified model indicated the intraparticle diffusion and pore wall adsorption were two closely linked processes. The initial concentration, the number of chlorine substitutions and the morphology structure of biochar were suggested to be the key factors affecting the adsorption of CBs on the biochar.

Sludge water (SW) arising from the dewatering of anaerobic digested sludge causes high back loads of ammonium, leading to high stress (inhibition of the activity of microorganisms by an oversupply of nitrogen compounds (substrate inhibition)) for wastewater treatment plants (WWTP). On the other hand, ammonium is a valuable resource to substitute ammonia from the energy intensive Haber-Bosch process for fertilizer production. Within this work, it was investigated to what extent and under which conditions Carpathian clinoptilolite powder (CCP 20) can be used to remove ammonium from SW and to recover it. Two different SW, originating from municipal WWTPs were investigated (SW1: c0 = 967 mg/L NH4-N, municipal wastewater; SW2: c0 = 718–927 mg/L NH4-N, large industrial wastewater share). The highest loading was achieved at 307 K with 16.1 mg/g (SW1) and 15.3 mg/g (SW2) at 295 K. Kinetic studies with different specific dosages (0.05 gCLI/mgNH4-N), temperatures (283–307 K) and pre-loaded CCP 20 (0–11.4 mg/g) were conducted. At a higher temperature a higher load was achieved. Already after 30 min contact time, regardless of the sludge water, a high load up to 7.15 mg/g at 307 K was reached, achieving equilibrium after 120 min. Pre-loaded sorbent could be further loaded with ammonium when it was recontacted with the SW.

This study investigates the adsorption performance of granular activated carbon (GAC) and pelletized activated carbon (PAC) for the purification of syngas produced from glycerol reforming, focusing on the removal of CO2, CO, and CH4. The adsorption process was studied at two different flow rates (0.5 L/min and 1 L/min) to assess the impact of particle size and gas flow rate on adsorption capacity. The results indicate that GAC exhibits superior multi-gas adsorption, particularly at lower flow rates, effectively capturing CO2, CO, and CH4, while PAC exhibits lower adsorption performance. Kinetic analysis revealed that the pseudo-second-order and Avrami models fit well with both adsorbents, though GAC aligns more closely with the Avrami model, reflecting its multi-step adsorption mechanism and greater pore diffusion efficiency. These findings highlight the importance of adsorbent size and flow rate in optimizing hydrogen purification processes, with GAC emerging as a highly efficient adsorbent for industrial-scale syngas treatment.

The adsorption of chlorpheniramine (CPA) on a series of activated carbon (AC) samples was investigated. Commercial AC Megapol M (MM) samples were reactivated with CO2 at 800 °C for different times. The ACs were designated as MM4, MM8, and MM8A, corresponding to 4, 8, and 8 h cumulative (4 h and 4 h), respectively. The textural properties of MM8A were the highest due to an additional CO2 reactivation process. Quantification of the carboxylic sites showed a decrease in the order MM > MM8A > MM4 > MM8. The Raman spectra of MM, MM4, MM8, and MM8A indicated that for longer CO2 reactivation times, the D to G band intensity ratio (ID/IG) of all ACs increased due to surface defects. The CPA-adsorption capacity of the ACs revealed that MM8A had the highest adsorption capacity, attributed to its low density of carboxylic sites and disordered structure. Increasing the pH solution enhanced the CPA adsorption on MM8A, while temperature had a minor effect. The isosteric heat of adsorption indicated the CPA adsorption on MM8A occurred via physical interactions, with π–π stacking and hydrophobic interactions governing the process at pH = 11. The rate of CPA adsorption on MM8A was studied using diffusional models. The external mass transport model satisfactorily estimated the experimental data. Finally, it was found that CPA adsorbed more rapidly on MM8A than on MM.

Methanol ammoxidation over FeMo/SiO2 has emerged as a promising low-temperature route to hydrogen cyanide (HCN). In this work, an eight-parameter Mars–van Krevelen (MvK) kinetic model, previously established from intrinsic fixed-bed experiments, is embedded in a heterogeneous plug-flow description to design an industrial multitubular reactor with a nominal HCN capacity of 10,000 t∙a−1. The reactor is represented by a bank of isothermal tubes that are operated at 420 °C and a mildly elevated pressure, each packed with spherical FeMo/SiO2 pellets. Detailed simulations for a 30 mm inner tube diameter and 2 mm pellets, including an Ergun pressure drop and intraparticle diffusion with realistic effective diffusivities, show that a 4 m bed at an outlet pressure of 1.5 bar (abs) achieves an essentially complete methanol conversion with a carbon-based HCN yield of ≈0.95 at a space time of ≈160 gcat∙h∙mol−1. Axial effectiveness factors remain above ≈0.6, indicating moderate but manageable diffusion limitations. Comparison with a 35 mm/3 mm geometry reveals a clear trade-off between pressure drop and HCN selectivity. Parametric studies of space time, feed composition and outlet pressure delineate a broad non-flammable operating window with robust HCN yield and moderate compression duty. The results demonstrate how a mechanistic MvK rate expression can be translated into a practical design framework for FeMo-based multitubular HCN reactors.

This study presents a comparative analysis of the adsorption behavior of three industrial ionic dyes—Indigo Carmine (IC), Congo Red (CR), and Evans Blue (EB)—using two adsorbent materials with distinct physicochemical and textural properties: bone char (BC) and activated carbon cloth (ACC). The main objective was to evaluate and compare the adsorption equilibrium and kinetics of these dyes on both materials. Equilibrium behavior was analyzed using the Prausnitz–Radke isotherm model, while adsorption kinetics were evaluated using PVSDM. The results showed that adsorption onto BC was primarily driven by electrostatic interactions, enhanced by the presence of hydroxyapatite. The maximum adsorbed amounts were determined to be 0.296, 0.107, and 0.0614 mmol g[sup.−1] for CR, IC, and EB, respectively. In contrast, adsorption on ACC was influenced by both electrostatic and hydrophobic forces due to its carbonaceous composition. IC exhibited significantly higher adsorption on ACC (1.087 mmol g[sup.−1]), whereas CR and EB only 0.269 mmol g[sup.−1] and 0.028 mmol g[sup.−1], respectively. Kinetic studies revealed that intraparticle transport was the rate-limiting step across all systems. Specifically, pore volume diffusion controlled the adsorption rate on ACC, with mean diffusion coefficients of 9.72 × 10[sup.−8], 1.83 × 10[sup.−9], and 1.48 × 10[sup.−10] cm[sup.2] s[sup.−1] for IC, CR and EB, respectively. Conversely, for BC, adsorption surface diffusion played a dominant role in the adsorption of IC and CR, with mean diffusion coefficients of 1.62 × 10[sup.−9] and 7.28 × 10[sup.−10] for IC and CR, respectively. These findings underscore the importance of considering both equilibrium and kinetic parameters in the design of efficient wastewater treatment systems.