Carboxylate-functionalized dragon fruit peel powder as an effective adsorbent for the removal of Rhodamine B (cationic dye) from aqueous solution: adsorption behavior and mechanism

In this study, we used a simple and low-toxicity chemical treatment to make a carboxylate-functionalized dragon fruit peel powder (CF-DFPP) from dragon fruit peel to improve its capacity for adsorbing Rhodamine B (RhB) from an aqueous medium. Field Emission-Scanning Electron Microscopy/Energy-Dispersive X-ray (FE-SEM/EDX), point of zero charges (pH_PZC), Brunauer-Emmett-Teller (BET), and Fourier Transform Infrared (FT-IR) analyses were performed to characterize the adsorbent materials. The adsorption performance and mechanism for the removal of RhB were examined. The kinetic, isotherm and thermodynamic parameters were employed to evaluate the adsorption mechanism. Compared to other models, the Langmuir isotherm and PSO kinetic models better defined the experimental data. CF-DFPP adsorbent exhibited a maximum adsorption efficiency of 228.7 mg/g at 298 K for RhB adsorption. Thermodynamic analysis revealed that the adsorption of RhB by CF-DFPP was spontaneous (ΔG^o < 0) and exothermic (ΔH^o < 0) nature of the process. Different eluting agents were used in desorption tests, and NaOH was revealed to have greater desorption efficiency (96.8%). Furthermore, regeneration examinations revealed that the biosorbent could effectively retain RhB, even after six adsorption/desorption cycles. These findings demonstrated that the CF-DFPP might be a novel material for removing RhB from an aqueous medium.

Removal of anionic (Acid Yellow 17 and Amaranth) dyes using aminated avocado (Persea americana) seed powder: adsorption/desorption, kinetics, isotherms, thermodynamics, and recycling studies

Aminated avocado seed powder (AASP)-an eco-friendly novel adsorbent has been used for the removal of Acid Yellow 17 (AY 17) and Amaranth (AMR) from an aqueous phase. The AASP (before and after adsorption) was systematically characterized by different analytical techniques such as FT-IR, FESEM, EDX, and N₂ adsorption-desorption analysis. Non-linear form of various kinetic (PFO and PSO) and isotherm (Langmuir and Freundlich) models were used to examine the adsorption behavior of AY 17 and AMR onto AASP. The adsorption of AY 17 and AMR onto AASP was well illustrated by the PSO kinetic model and Langmuir isotherm models. At 303 K, the maximum adsorption capacities (obtained from the Langmuir) of the AASP for AY 17 and AMR was 42.7 and 89.2 mg/g, respectively. The AY 17 and AMR adsorption was strongly pH-dependent with an optimum pH value of 2.0. Activation energy was calculated as 12.3 and 16.3 kJ/mol for AY 17 and AMR respectively, suggesting physical adsorption. The positive values of ΔG^o and ΔH^o indicated that the adsorption process of AY 17 and AMR onto AASP was non-spontaneous and endothermic. The negligible loss of adsorption capacity and excellent regeneration of AASP were observed for the five cycles. Statement of novelty: The present research majorly focused on the synthesis of adsorbent from Avocado seed for the removal of Acid Yellow 17 and Amaranth anionic dyes from aqueous solution. Although the literature is available on direct seed powder as adsorbent, to the best of our knowledge, no chemical modified adsorbent synthesis was not available. Hence, to fill the gap in the literature, we chose the following study that significantly enhanced the adsorption efficiency of the selected anionic dyes.

Adsorptive removal of copper and nickel ions from water using chitosan coated PVC beads

A new biosorbent was developed by coating chitosan, a naturally and abundantly available biopolymer, on to polyvinyl chloride (PVC) beads. The biosorbent was characterized by FTIR spectra, porosity and surface area analyses. Equilibrium and column flow adsorption characteristics of copper(II) and nickel(II) ions on the biosorbent were studied. The effect of pH, agitation time, concentration of adsorbate and amount of adsorbent on the extent of adsorption was investigated. The experimental data were fitted to Langmuir and Freundlich adsorption isotherms. The data were analyzed on the basis of Lagergren pseudo first order, pseudo-second order and Weber-Morris intraparticle diffusion models. The maximum monolayer adsorption capacity of chitosan coated PVC sorbent as obtained from Langmuir adsorption isotherm was found to be 87.9 mg g(-1) for Cu(II) and 120.5 mg g(-1) for Ni(II) ions, respectively. In addition, breakthrough curves were obtained from column flow experiments. The experimental results demonstrated that chitosan coated PVC beads could be used for the removal of Cu(II) and Ni(II) ions from aqueous medium through adsorption.