Nonlinear Analysis of the Kinetics and Equilibrium for Adsorptive Removal of Cd(II) by Starch Phosphate

Adsorption of the non-steroidal anti-inflammatory drug (ibuprofen) onto biochar and magnetic biochar prepared from chrysanthemum waste of the beverage industry

Biochar and magnetic biochar prepared from chrysanthemum waste of the beverage industry are effective adsorbents for the removal of the non-steroidal anti-inflammatory drug, ibuprofen (IBP), from aqueous systems. The development of magnetic biochar using iron chloride, overcame poor separation characteristics from the liquid phase of the powdered biochar after adsorption. Characterisation of biochars was achieved through Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), N₂ adsorption/desorption porosimetry, scanning electron microscopy (SEM), electron dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), moisture and ash content, bulk density, pH and zero-point charge (pH_pzc). The specific surface area of non-magnetic and magnetic biochars was 220 and 194 m² g^-1, respectively. Adsorption of ibuprofen was optimised with respect to contact time (5-180 min), solution pH (2-12) and initial drug concentration (5-100 mg L^-1), with equilibrium being reached in 1 hour, and the maximum ibuprofen removal occurred at pH 2 and 4 for biochar and magnetic biochars, respectively. Investigation of the adsorption kinetics was achieved through application of the pseudo-first order, pseudo-second order, Elovich and intra-particle diffusion models. Adsorption equilibrium was evaluated using Langmuir, Freundlich and Langmuir-Freundlich isotherm models. The adsorption kinetics and isotherms for both biochars are well described by pseudo-second order kinetic and Langmuir-Freundlich isotherm models, respectively, with the maximum adsorption capacity of biochar and magnetic biochar being 167 and 140 mg g^-1, respectively. Chrysanthemum derived non-magnetic and magnetic biochars exhibited significant potential as sustainable adsorbents toward the removal of emerging pharmaceutical pollutants such as ibuprofen from aqueous solution.

Easy and Low-Cost Method for Synthesis of Carbon–Silica Composite from Vinasse and Study of Ibuprofen Removal

Vinasse was successfully utilized to synthesize carbon–silica composite with a low-cost silica source available in Thailand (sodium silicate, Na2SiO3) and most commonly used source, tetraethyl orthosilicate (TEOS). The composites were prepared by a simple one-step sol–gel process by varying the vinasse (as carbon source) to silica source (Na2SiO3 or TEOS) weight ratio. The resulting composites were characterized by N2 adsorption, moisture and ash contents, pH, pHpzc, bulk density, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX). The composites had highest surface area of 313 and 456 m2/g, with average mesopore diameters of 5.00 and 2.62 nm when using Na2SiO3 and TEOS as the silica sources, respectively. The adsorption of a non-steroidal anti-inflammatory drug, ibuprofen, was investigated. The contact time to reach equilibrium was 60 min for both composites. The adsorption kinetics were fitted by a pseudo-second-order model with the correlation coefficient R2 > 0.997. The adsorption isotherms were well described by the Langmuir model (R2 > 0.992), which indicates monolayer adsorption. The maximal adsorption capacities of the Na2SiO3- and TEOS-based composites were as high as 406 and 418 mg/g at pH 2, respectively. The research results indicate that vinasse and a low-cost silica source (Na2SiO3) show great potential to synthesize adsorbents through a simple method with high efficiency.

Preparation of Rosin-Based Composite Membranes and Study of Their Dencichine Adsorption Properties

In this work, rosin-based composite membranes (RCMs) were developed as selective sorbents for the preparation of dencichine for the first time. The rosin-based polymer microspheres (RPMs) were synthesized using 4-ethylpyridine as a functional monomer and ethylene glycol maleic rosinate acrylate as a crosslinking. RCMs were prepared by spinning the RPMs onto the membranes by electrostatic spinning technology. The optimization of various parameters that affect RCMs was carried out, such as the ratio concentration and voltage intensity of electrospinning membrane. The RCMs were characterized by SEM, TGA and FT-IR. The performances of RCMs were assessed, which included adsorption isotherms, selective recognition and adsorption kinetics. The adsorption of dencichine on RCMs followed pseudo-second-order and adapted Langmuir–Freundlich isotherm model. As for the RCMs, the fast adsorption stage appeared within the first 45 min, and the experimental maximum adsorption capacity was 1.056 mg/g, which is much higher than the previous dencichine adsorbents reported in the literature. The initial decomposition temperature of RCMs is 297 °C, the tensile strength is 2.15 MPa and the elongation at break is 215.1%. The RCMs have good thermal stability and mechanical properties. These results indicated that RCMs are a tremendously promising adsorbent for enriching and purifying dencichine from the notoginseng extracts.

The adsorptive behaviour of kaolinite to sodium dodecyl benzene sulphonate and the structural variation of kaolinite

Analysis of the adsorptive behaviour of kaolinite to sodium dodecyl benzene sulphonate (SDBS) at different concentrations can provides a basis for selecting the best concentration. The adsorptive capacity and adsorptive behaviour of kaolinite to SDBS at different concentrations were studied using ultraviolet spectrophotometer, pseudo-first-order adsorption kinetics model, and pseudo-second-order adsorption kinetics model. Scanning electron microscopy with energy dispersive spectrometry (SEM–EDS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR) were used to study the variation characteristics of surface structure, crystallinity indices, and main functional groups on kaolinite before, and after, adsorption. The results show that as the SDBS concentration increase, the adsorptive capacity of kaolinite to SDBS increase. The adsorption process can be accurately fitted by the pseudo-secondary adsorption kinetic model, which means the adsorptive behaviour was mainly chemical in origin. The adsorption of SDBS by kaolinite mainly occurs on the surface. The solidification, lamellar aggregation, and crystallinity index of kaolinite are more obvious after the adsorption of SDBS, but the interlayer spacing of kaolinite did not change to any significant. After the adsorption of SDBS, the intensity ratio of 1000–1008 cm⁻¹ bands changed significantly, indicating the change of the chemical environment, and the adsorptive behaviour was chemical.

Hierarchical multi-shell hollow micro-meso-macroporous silica for Cr(VI) adsorption

The development of easier, cheaper, and more effective synthetic strategies for hierarchical multimodal porous materials and multi-shell hollow spheres remains a challenging topic to utilize them as adsorbents in environmental applications. Here, the hierarchical architecture of multi-shell hollow micro–meso–macroporous silica with pollen-like morphology (MS-HMS-PL) has been successfully synthesized via a facile soft-templating approach and characterized for the first time. MS-HMS-PL sub-microspheres showed a trimodal hierarchical pore architecture with a high surface area of 414.5 m² g⁻¹, surpassing most of the previously reported multishelled hollow nanomaterials. Due to its facile preparation route and good physicochemical properties, MS-HMS-PL could be a potential candidate material in water purification, catalysis, and drug delivery. To investigate the applicability of MS-HMS-PL as an adsorbent, its adsorption performance for Cr(VI) in water was evaluated. Important adsorption factors affecting the adsorption capacity of adsorbent were systematically studied and Kinetics, isotherms, and thermodynamics parameters were computed via the non-linear fitting technique. The maximum capacity of adsorption computed from the Langmuir isotherm equation for Cr(VI) on MS-HMS-PL was 257.67 mg g⁻¹ at 293 K and optimum conditions (pH 4.0, adsorbent dosage 5.0 mg, and contact time 90 min).

Synthesis of MgO micro-rods coated with charred dextrose and its application for the adsorption of selected heavy metals from synthetic and real groundwater

MgO micro-rods supported on porous carbon were synthesized by an economical method and applied for the adsorption of three different heavy metals ions (As (III), Cd (II) and Pb (II)). Here, we used dextrose as the source of carbon during the synthesis. The synthesized material has been characterized by different techniques like XRD, TEM, FE-SEM, BET and FT-IR for the determination of various physical properties. Compared with MgO synthesized without dextrose, the carbon-supported MgO or C-MgO demonstrated consistent rod-shaped morphology, higher surface area and better absorptivity. The adsorption data were analysed using various isotherm models and the Freundlich isotherm model seemed to provide the best fit to the data. The adsorption kinetics data on the other hand was well explicated by the pseudo second-order kinetic model. The maximum adsorption capacity of C-MgO was 508.47 mg g^-1 for As (III), 566.01 mg g^-1 for Cd (II) and 476.19 mg g^-1 for Pb (II), respectively after 6 h of reaction. To check the real-life usability and efficiency of C-MgO, it was added to a groundwater sample which had 169.55 ppb of As (III) and within 20 min it was adsorbed with 99% efficiency. Reusability studies reveal that C-MgO could be used up to 6 times with more than 60% efficiency. This study shows that C-MgO has high adsorptive ability, is an economic and non-toxic material with versatile applications and can be used for groundwater remediation in real life.

Acidic surface functional groups control chemisorption of ammonium onto carbon materials in aqueous media

Elucidation of mechanistic insight into the interaction of carbon materials' physicochemical surface properties and ammonium (NH₄⁺) adsorption in aqueous media was made by conducting a systematic study using a wide range of carbon materials. Three types of biochars (rice husk, poultry litter, and enhanced poultry litter) and activated carbons (fresh and aged coconut shell-based and charcoal-based) were used for investigating the NH₄⁺ adsorption mechanism. Poultry litter biochar, with lowest surface area (3 m² g^-1) and largest pore diameter (29 nm), showed the highest NH₄⁺ adsorption capacity (0.34 mg NH₄⁺g^-1), while charcoal-based activated carbon, with the highest surface area (1133 m² g^-1) and small pore diameter (6 nm), had the least NH₄⁺ adsorption capacity (0.09 mg NH₄⁺g^-1). The value of Freundlich isotherm constant 'n' was >1 for all tested carbon materials indicating chemisorption as the dominant sorption mechanism. Aging of the carbon surface resulted in 30% increase in NH₄⁺ retention. Surface chemical properties that most influenced NH₄⁺ chemisorption on to carbon materials were found to be acidic surface functional groups (ASFGs), elemental composition, ash content, and pH. The optimal conditions for NH₄⁺ adsorption, regardless of type and source of carbon materials, were solution pH of 8, a high amount of ash content, and carboxyl, carbonyl, and phenolic functional groups. Evaluation of CEC and ASFGs indicated that CEC and ASFGs are not equivalent terms. Through this study, conducted on carbon adsorbents derived from different sources, with different surface physical and chemical properties, we established that ASFGs, and not CEC, play a critical role in ammonium chemisorption on carbon materials. The study showed that low cost and eco-friendly biochars, with optimal surface chemistry, can replace expensive activated carbons for NH₄⁺ remediation in aqueous media.