Hydrogel‐biochar composites for removal of methylene blue: Adsorption performance, characterization, and adsorption isotherm, kinetics, thermodynamics analysis

Abstract

Low‐concentration organic dye wastewater severely threatens the growth and reproduction of animals and plants, as well as the survival and development of human beings and the environment. Although versatile hydrogel composites have been prepared owing to their excellent adsorption performance, the high‐removal efficiency and fast adsorption rate are still two crucial problems related to practical applications. Herein, xanthan gum‐g‐poly (acrylic acid‐co‐acrylamide)/biochar composite hydrogels with high‐removal efficiency and fast adsorption rate of methylene blue (MB) are synthesized using sodium dodecyl sulfate as a pore‐foaming agent. The composite hydrogels exhibit rough and porous three‐dimensional structures, which can make the internal active adsorption sites to be fully exposed and facilitate the MB diffusion process. MB's removal efficiency can reach 96.64% within 30 minutes, which is almost the first time that a biochar‐contained hydrogel could show superior removal efficiency of more than 95% in such a short adsorption time. The factors affecting the adsorption performance are studied comprehensively. Langmuir and pseudo‐second‐order models fit the adsorption process well. Moreover, the MB removal rate still exceeds 80% after eight cycles, which is also a vital indicator for practical treatment. Adsorption mechanism analysis shows that the synergistic effect among biochar, xanthan gum, and polymer chains and the porous structure improve the adsorption performance of the composite hydrogels. The proposed hydrogel‐biochar composites with high‐removal efficiency and adsorption rate are highly promising as an alternative adsorbent for advanced printing and dyeing wastewater treatment.

Preparation of a cationic hydrogel microsphere adsorbent for efficient removal of hexavalent chromium from aqueous solution

“…[10][11][12] Due to their large adsorption capacity, unique environmental sensitivity, and selective adsorption ability, hydrogel adsorbents have been widely employed to remove pollutants in wastewater, such as synthetic dyes, heavy metals, phenols, and phosphorus pollutants. 10,13,14 Relevant studies demonstrate that the mass transfer process of the pollutants can be divided into two steps: first, the pollutants transport from the aqueous phase to the hydrogel adsorbent's surface; second, the pollutants diffuse in the hydrogel matrix. Some pollutants will be adsorbed by active adsorption sites on the hydrogel's surface, while others will permeate the hydrogel and be captured by the sites within the hydrogel network.…”

“…Some pollutants will be adsorbed by active adsorption sites on the hydrogel's surface, while others will permeate the hydrogel and be captured by the sites within the hydrogel network. 10,14 These two steps correspond to surface adsorption and diffusion adsorption, respectively. As a result, although many hydrogel adsorbents do not have the porous structure like activated carbon, their surface and internal adsorption sites can be both employed to adsorb pollutants in water, giving them comparable adsorption capacities to typical porous adsorbents.…”

“…Hydrogels are polymer materials with a three‐dimensional network structure and a high concentration of hydrophilic groups 10–12 . Due to their large adsorption capacity, unique environmental sensitivity, and selective adsorption ability, hydrogel adsorbents have been widely employed to remove pollutants in wastewater, such as synthetic dyes, heavy metals, phenols, and phosphorus pollutants 10,13,14 . Relevant studies demonstrate that the mass transfer process of the pollutants can be divided into two steps: first, the pollutants transport from the aqueous phase to the hydrogel adsorbent's surface; second, the pollutants diffuse in the hydrogel matrix.…”

“…Relevant studies demonstrate that the mass transfer process of the pollutants can be divided into two steps: first, the pollutants transport from the aqueous phase to the hydrogel adsorbent's surface; second, the pollutants diffuse in the hydrogel matrix. Some pollutants will be adsorbed by active adsorption sites on the hydrogel's surface, while others will permeate the hydrogel and be captured by the sites within the hydrogel network 10,14 . These two steps correspond to surface adsorption and diffusion adsorption, respectively.…”