An investigation on the adsorption and removal performance of a carboxymethylcellulose-based 4-aminophenazone@MWCNT nanocomposite against crystal violet and brilliant green dyes

ZnO@ activated carbon derived from wood sawdust as adsorbent for removal of methyl red and methyl orange from aqueous solutions

Activated carbon (AC) and ZnO@AC composite derived from wood sawdust were prepared to be utilized as adsorbents for methyl red (MR) and methyl orange (MO) anionic dyes from the aqueous solutions. The maximum adsorption capacity of the AC and ZnO@AC composite toward both dyes was achieved in the strong acidic medium (pH = 3), and under stirring for 60 min. The kinetic studies revealed that the adsorption of MR and MO dyes onto the AC and ZnO@AC composite fitted well with the pseudo-second-order model. Furthermore, the intraparticle diffusion and Elovich kinetic models confirmed the adsorption is controlled by external surfaces, and the adsorption is chemisorption process. The isotherm results indicated that the MR and MO dye adsorption occurred via monolayer adsorption, and the estimated maximum adsorption capacities of both dyes onto the ZnO@AC composite were higher than those achieved by AC. Thermodynamic analysis suggested that the adsorption is endothermic and spontaneous. The mechanism for MR, and MO dyes adsorption onto the AC and ZnO@AC composite is proposed to be controlled by electrostatic bonding, π-π interactions, and ion exchange, while H-bonding and n-π interactions were minor contributors. This study reveals the potential use of carbon-based adsorbents derived from wood sawdust for the removal of anionic dyes from wastewater.

Iodide ion-imprinted chitosan beads for highly selective adsorption for nuclear wastewater treatment applications

Iodide ions from radioactive iodine isotopes are common contaminants present in nuclear wastewater from nuclear power plants which are considered hazardous contaminants to be released in water sources even at low concentrations due to their association with metabolic disorders, therefore its removal from the nuclear wastewater effluents is necessary. Chitosan beads are natural and cost-efficient adsorbents that have been used for ion removal from wastewater. However, issues of poor selectivity persist in achieving high-efficiency iodide ion removal. In this study, ion-imprinted chitosan beads (IIC) have been synthesized using the phase-inversion method, IIC beads were modified by cross-linking with epichlorohydrin (IIC-EPI) and modified by cross-linking with epichlorohydrin and silicon dioxide nanoparticles (IIC-SiO2-EPI). Through 4 h of batch adsorption experiments, IIC beads achieved a maximum adsorption capacity (Qe) of 0.65 mmol g-1 and showed more preference for the iodide ions compared to the non-imprinted chitosan beads which achieved a maximum adsorption capacity of 0.27 mmol g-1 at pH 7. While the modified beads IIC-EPI and IIC-SiO2-EPI beads have boosted the adsorption capacities to 0.72 mmol g-1 and 0.91 mmol g-1. Scanning electron microscopic cross-sectional images have shown more pores and cavities than the surface images which agrees with the multilayer heterogeneous diffusion suggested by the Freundlich adsorption isotherm, that the experimental data has fitted. Adsorption kinetic data have fitted the Pseudo-second-order model as well as the Weber and Morris intraparticle model, which suggest an intraparticle pore diffusion adsorption mechanism, with the involvement of the physical electrostatic interactions with the cationic chitosan surface.

Exploitation of expired cellulose biopolymers as hydrochars for capturing emerging contaminants from water

Expired chemicals pose a potential environmental threat to humans and living organisms. Herein, we proposed a green approach whereby expired cellulose biopolymers were converted to hydrochar adsorbents and tested for removing the emerging pharmaceutical contaminants of fluoxetine hydrochloride and methylene blue from water. A thermally stable hydrochar was produced with an average particle size of 8.1 ± 1.94 nm and a mesoporous structure that exhibited a larger surface area than the expired cellulose by 6.1 times. The hydrochar was efficient in removing the two contaminants with efficiencies that reached above 90% under almost neutral pH conditions. Adsorption exhibited fast kinetics and regeneration of the adsorbent was successful. The adsorption mechanism was hypothesized in view of the Fourier Transform Infra-Red (FTIR) spectroscopy and pH effect measurements to be mainly electrostatic. A hydrochar/magnetite nanocomposite was also synthesized, and its adsorption behavior for both contaminants was tested and it revealed an enhanced percent removal relative to the bare hydrochar by 27.2% and 13.1% for FLX and MB, respectively. This work supports the strategies for zero waste management and the circular economy.