The aim of this study was to optimize the adsorption performance of activated carbon (AC), derived from the shell of Penaeus vannamei prawns, on heavy metal ions. Inexpensive, non-toxic, and renewable prawn shells were subjected to carbonization and, subsequently, KOH-activation to produce nanoporous K-Ac. Carbonized prawn shells (CPS) and nanoporous KOH-activated carbon (K-Ac) from prawn shells were prepared and characterized by FTIR, XRD, BET, SEM, and TEM. The results showed that as-produced K-Ac samples were a porous material with microporous and mesoporous structures and had a high specific surface area of 3160 m²/g, average pore size of about 10 nm, and large pore volume of 2.38 m³/g. Furthermore, batches of K-Ac samples were employed for testing the adsorption behavior of Cd²⁺ in solution. The effects of pH value, initial concentration, and adsorption time on Cd²⁺ were systematically investigated. Kinetics and isotherm model analysis of the adsorption of Cd²⁺ on K-Ac showed that experimental data were not only consistent with the Langmuir adsorption isotherm, but also well-described by the quasi-first-order model. Finally, the adsorption behaviors of as-prepared K-Ac were also tested in a ternary mixture of heavy metal ions Cu²⁺, Cr⁶⁺, and Cd²⁺, and the total adsorption amount of 560 mg/g was obtained.

This study, for the first time, rendered crab shell activated biochar modified by potassium hydroxide (KOH) impregnation (CSAB), revealing a new potential application in the removal of diesel oil from oily wastewater. The structural characteristics of crab shell biochar (CSB) and CSAB were investigated by SEM, and the crystal structure and optical properties of as-prepared samples were analyzed using XRD and FTIR. Results showed that CSAB had stratified surface structure morphology, abundant functional groups, and that its high specific surface area could reach up to 2441 m²/g, which was about eight times larger than that of untreated CSB (307 m²/g). An adsorption isotherm study indicated that the actual adsorption process both of CSAB and CSB were found to fit better with the Freundlich equation. Moreover, chemical interaction controlled the adsorption kinetics efficiency while the adsorption equilibrium capacity was 93.9 mg/g. Due to its highly developed pore structure, unique surface characteristics, and effective adsorption performance, this low-cost activated carbon had the potential to serve as an efficient adsorbent for water pollution purification.

In response to an increasing desire for modern industries to be both green and sustainable, there has been increasing research focus on the reutilization of natural waste materials to effectively remove and degrade toxic wastewater effluents. One interesting food industry waste product is clam shell. Here a new photocatalytic nanomaterial derived from marine clam shells was successfully prepared and characterized. Thereafter the material was applied for the removal of two target dyes from aqueous solution, where the effect of both catalyst dose and initial dye concentration on adsorption and photocatalysis was investigated. The maximum adsorption capacities of methylene blue (100 mg/L) and Congo red (500 mg/L) were 123.45 mg/g and 679.91 mg/g, respectively, where adsorption followed pseudo second order kinetics predominantly via a chemical adsorption process. The photodegradation removal efficiencies of the two dye solutions under visible light irradiation were 99.6% and 83.3% for MB and CR, respectively. The excellent degradation performance in a mixed dye solution, with strong degradation capability and low cost, demonstrated that the clam shell catalyst material was a good candidate for practical field remediation of dye contaminated wastewater.

In this study, carbonized kelp biochar (AKB) modified by KOH impregnation and photocatalytic Bi₂MoO₆/AKB composite (BKBC) nanomaterials were the first time successfully synthesized for efficient removal of dyes in aqueous solution. BET, XRD, FT-IR, and SEM were employed to characterize as-prepared samples. UV-vis and other test results indicated that the removal efficiency of methylene blue (MB) was 61.39% and 94.12% for BKBC and AKB, respectively, which was up to 13 times and 20 times higher in comparison with pure Bi₂MoO₆ (PBM). In addition, the equilibrium adsorption capacity of MB could reach up to 324.1 mg/g for AKB. This high dyes adsorption performance could be likely attributed to its high specific surface area (507.177 m²/g) and its abundant presence of various functional groups such as –OH and =C–H on AKB. Particularly, the existing of amorphous carbon and transition metal oxides, such as Fe₂O₃ and Mn₅O₈, could be beneficial for the photodegradation of MB for AKB. Meanwhile, experimental data indicated that adsorption kinetics complied with the pseudo-second order model well, and all of the tests had satisfactory results in terms of the highly efficient adsorption and photodegradation activity of AKB nanomaterials, which suggested its great potential in wastewater treatment.