Adsorption of Nitrite Ions Using Activated Carbons Derived from Walnut Shells | Chapter 3 | Chemical and Materials Sciences: Research Findings Vol. 3

In this paper, activated carbons obtained from walnut shells were used as adsorbents to remove nitrite ions from aqueous solutions. In the Republic of Moldova, walnut shells are chosen as a raw material for obtaining activated carbons in research due to their local abundance, low cost, and favorable chemical composition, which allows for the production of an efficient adsorbent material for removing pollutants from water. The novel adsorbent was obtained by modification with hydrochloric acid. The physical-chemical characteristics of activated carbons were determined from nitrogen sorption isotherms, SEM-EDX, elemental analysis, FTIR, thermal analysis, and temperature-programmed decomposition (TPD). According to the results obtained, chlorine is retained on the surface in an amount of 2%. Chlorine increases the positive charge of the surface by forming –C–Cl or –C–OH⁺ groups, the electrostatic attraction towards nitrite ions can be improved, thus increasing the adsorption efficiency. The effect of pH on the adsorption of nitrite ions was investigated for both activated carbons CAN and CAN-Cl. For activated carbon CAN, an increase in pH resulted in a significant decrease in adsorption, from 0.13 mg/g at pH 3 to 0.07 mg/g (approximately 1.8 times lower). Similarly, for activated carbon CAN-Cl, adsorption values decreased from 2.85 mg/g to 0.68 mg/g as the pH increased. These results suggest that pH plays a critical role in the adsorption capacity of activated carbons, with lower pH levels enhancing the adsorption of nitrite ions. The results of batch experiments indicate that maximum adsorption/ removal of nitrite ions can be achieved at pH = 3, being of 0.2 mg/g for CAN and 4.7 mg/g for CAN-Cl. The modification of the surface of activated carbons with chloride ions leads to an increase in the rate and adsorption capacity of nitrite ions by approximately 50 times.

To study the adsorption of nitrite ions on activated carbons the following mathematical models were used: pseudo-first-order, pseudo-second-order, and intraparticle diffusion kinetic models, and Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin-Pyzhev isotherm models. These models were chosen to provide a comprehensive understanding of the adsorption kinetics and equilibrium behavior, allowing for the identification of the dominant adsorption mechanisms and the efficiency of the adsorbent material. The results indicate that the adsorption of nitrite ions onto activated carbons CAN and CAN-Cl follows the pseudo-second-order kinetic model and also aligns with the intraparticle diffusion model, suggesting that the process is primarily governed by chemisorption.

Future studies should explore strategies to mitigate the impact of electrolytes on adsorption efficiency and optimize surface modifications to enhance nitrite ion removal. Additionally, investigating the regeneration potential of the modified adsorbents could improve their practicality for long-term water treatment applications.

 

Author (s) Details

 

Irina Ceban
Institute of Chemistry, Moldova State University, 3, Academiei Str., MD-2028 Chisinau, Republic of Moldova.

Raisa Nastas
Institute of Chemistry, Moldova State University, 3, Academiei Str., MD-2028 Chisinau, Republic of Moldova.

 

 

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