Treated activated carbon as a metal-free catalyst for effectively catalytic reduction of toxic hexavalent chromium

Two-stage hydrothermal oxygenation for efficient removal of Cr(VI) by starch-based polyporous carbon: Wastewater application and removal mechanism

Cr(VI) is of concern because of its high mobility and toxicity. In this work, a two-stage hydrothermal strategy was used to activate the O sites of starch, and by inserting K-ion into the pores, starch-based polyporous carbon (S-PC) adsorption sites was synthesized for removal of Cr(VI). Physicochemical characterization revealed that the O content of the S-PC reached 20.66 % after activation, indicating that S-PC has excellent potential for adsorption of Cr(VI). The S-PC removal rate for 100 mg/L Cr(VI) was 96.29 %, and the adsorption capacity was 883.86 mg/g. Moreover, S-PC showed excellent resistance to interference, and an equal concentration of hetero-ions reduced the activity by less than 5 %. After 8 cycles of factory wastewater treatment, the S-PC maintained 81.15 % of its original activity, which indicated the possibility of practical application. Characterization and model analyses showed that the removal of Cr(VI) from wastewater by the S-PC was due to CC, δ-OH, ν-OH, and C-O-C groups, and the synergistic effect of adsorption and reduction was the key to the performance. This study provides a good solution for treatment of Cr(VI) plant wastewater and provides a technical reference for the use of biological macromolecules such as starch in the treatment of heavy metals.

Enhancement of Cr(VI) adsorption on lignin-based carbon materials by a two-step hydrothermal strategy: Performance and mechanism

Cr(VI) is a carcinogenic heavy metal that forms an oxygen-containing anion, which is difficult to remove from water by adsorbents. Here, industrial alkali lignin was transformed into a Cr(VI) adsorbent (N-LC) by using a two-step hydrothermal strategy. The characterization results of the adsorbent showed that O and N were uniformly distributed on the surface of the adsorbent, resulting in a favorable morphology and structure. The Cr(VI) adsorption of N-LC was 13.50 times that of alkali lignin, and the maximum was 326.10 mg g-1, which confirmed the superiority of the two-step hydrothermal strategy. After 7 cycles, the adsorption of N-LC stabilized at approximately 62.18 %. In addition, in the presence of coexisting ions, N-LC showed a selective adsorption efficiency of 85.47 % for Cr(VI), which is sufficient to support its application to actual wastewaters. Model calculations and characterization showed that N and O groups were the main active factors in N-LC, and CO, -OH and pyridinic-N were the main active sites. This study provides a simple and efficient method for the treatment of heavy metals and the utilization of waste lignin, which is expected to be widely applied in the environmental, energy and chemical industries.

Efficient Cr(vi) removal by expanded graphite synergized with oxalic acid under UV irradiation

Expanded graphite (EG), an easily-obtained carbon material with the potential of transferring electrons, was utilized successfully in the removal of hazardous hexavalent chromium (Cr(vi)) by environment-friendly oxalic acid (Ox) under UV irradiation. EG with a unique worm-like structure was obtained via a facile microwave treatment. The results showed that the EG + Ox + UV system had optimum performance, removing 99.32% of the Cr(vi) (1 mM) within 60 min at pH = 3, and the kinetic rate constant of Cr(vi) elimination was 7.95 mol L^-1 min^-1. Three components are potentially involved in the Cr(vi) elimination mechanism by the EG + Ox + UV system: (1) the direct electron transfer (DET) pathway of the EG-Ox-Cr(vi) through the acceleration effect of EG caused the majority removal of Cr(vi) under UV; (2) ·CO₂ ^- generated from Ox photolysis was used to reduce some Cr(vi); (3) ·CO₂ ^- created from Cr(vi)-Ox complexes in the solution through the photoinduced electron transfer (PET) pathway also reduced a little Cr(vi). Overall, the efficient removal of Cr(vi) by the EG + Ox + UV system provided new ideas for future research on Cr(vi) treatment.

Synthesis of Activated Porous Carbon from Red Dragon Fruit Peel Waste for Highly Active Catalytic Reduction in Toxic Organic Dyes

In this study, an alternative precursor for production of biomass-derived activated carbon was introduced using dragon fruit (Hylocereus costaricensis) peels. Chemical activators such as FeCl3, MgCl2, ZnCl2 were used in the thermal carbonization process to convert carbon into porous carbon (PC). However, heteroatom-doped PC catalysts including N-, B-, and P-doped carbon catalysts in the field of dye removal is highly desirable. Several approaches (XRD, FE-SEM/TEM, XPS, FT-IR, EDS, and elemental mapping) were employed to examine the surface morphology, surface properties, and elemental composition of the PC catalyst. The catalytic activity of metal-free PC catalyst was demonstrated for methylene blue (MB), crystal violet (CV), and Nile blue (NB) in a mild environment The corresponding rate constant (kapp) values were estimated as 0.2473, 0.3248, and 0.3056 min−1, respectively, for MB, CV, and NB, which were significantly greater than those of numerous reports. It exhibited the best catalytic activity and recyclability. Moreover, the approach proposed here could create new opportunities for the remediation of organic dyes in lakes and industrial wastewater.

Recyclable Mussel-Inspired Magnetic Nanocellulose@Polydopamine-Ag Nanocatalyst for Efficient Degradation of Refractory Organic Pollutants and Bacterial Disinfection

Development of a novel strategy to tackle bacterial-contaminated complex industrial wastewaters containing refractory organic pollutants is of great demand. In this study, polydopamine (PDA)-coated magnetic cellulose nanofiber (MCNF)-loaded silver nanoparticle (AgNP) (MCNF/PDA-Ag) nanocomposites were designed and applied for efficient degradation of organic dye pollutants and inactivation of Escherichia coli (E. coli) in wastewater. In the presence of NaBH₄, MCNF/PDA-Ag could achieve a high catalytic reduction rate of 6.54 min^-1 for the removal of methylene blue. Similarly, it showed good catalytic reduction performance for methyl orange (0.63 min^-1) and 4-nitrophenol (2.94 min^-1). The MCNF/PDA-Ag nanocomposites can be easily magnetically recycled and reused with negligible loss of catalytic performance. Moreover, this nanocatalyst also exhibited excellent disinfection performance against E. coli, with more than 99% disinfection ratio at very low doses (50 μg/mL). Overall, this work provides new insights into a delicate design of advanced magnetically recyclable silver nanocomposites with ultrahigh catalytic rates and excellent antibacterial properties from sustainable nature biomass.