Waste tire heat treatment to prepare sulfur self-doped char via pyrolysis and K2FeO4-assisted activation methods

Synthesis of porous carbon derived from coal tar residue via bimetallic salt activation for effective and selective adsorption of thallium(I)

As a highly toxic rare metal, the removal of thallium (Tl) from wastewater has been widely investigated, and adsorption is considered one of the most promising treatment technologies for Tl-containing contaminated water because of its cost-effectiveness, convenience, and high efficacy. In this work, coal tar residue (CTR)-based porous carbon was synthesized through K2FeO4 activation, and applied in adsorbing Tl(I). K2FeO4 could synergistically produce porosity and load iron oxide on the produced porous carbon surface because of the catalytic cracking and oxidative etching during the activation of CTR. The adsorbent was synthesized at 800 ℃ with a mass ratio of K2FeO4/CTR being 3 (PC3-800) showed optimal Tl(I) adsorption performance. The removal efficiency and distribution coefficient of PC3-800 were above 95 % and 104 mL/g, respectively, in a wide pH range (4-10). Furthermore, the selection and reusability of PC3-800 were favorable. The adsorption was a spontaneous, exothermic, and entropy increase process. The adsorption process was dominated by electrostatic attraction, surface complexation, and surface oxidation. The results suggested that removing Tl(I) from contaminated water via CTR-based porous carbon was feasible.

Fe/N codoped porous graphitic carbon derived from macadamia shells as an efficient cathode oxygen reduction catalyst in microbial fuel cells

In this study, Fe/N codoped porous graphitic carbon derived from macadamia shells was prepared at different temperatures as cathodic catalysts for microbial fuel cells (MFCs), with K₂FeO₄ as a bifunctional catalyst for porosity and graphitization. The catalyst prepared at 750 °C (referred to as MSAC-750) showed a large specific surface area (1670.3 m² g^-1), graphite structure, and high pyridine-N and Fe-N _X contents. Through the electrochemical workstation test, MSAC-750 shows excellent oxygen reduction reaction (ORR) activity, with an onset potential of 0.172 V and a half-wave potential of -0.028 V (vs. Ag/AgCl) in a neutral medium, and the ORR electron transfer number is 3.89. When applied to the MFCs as cathodic catalysts, a higher maximum power density and voltage of 378.68 mW m^-2 and 0.425 V were achieved with the MSAC-750 catalyst and is superior to that of the Pt/C catalyst (300.85 mW m^-2 and 0.402 V). In this case, a promising method is hereby established for the preparation of an excellent electrochemical catalyst for microbial fuel cells using inexpensive and easily available macadamia shells.

Evaluation of potassium ferrate activated biochar for the simultaneous adsorption of copper and sulfadiazine: Competitive versus synergistic

Combined pollution caused by organic pollutants and heavy metals pose a significant challenge to the adsorption process. In this study, iron-modified biochar (Fe-BC) was prepared by using ferrate (K₂FeO₄) and wheat stalk as the precursors for the adsorption of copper (Cu²⁺) and sulfadiazine (SDZ), especially under combined pollution scenarios. Iron modification not only enlarged the surface area but also loaded iron oxide nanoparticles on biochar surface. Accordingly, Fe-BC exhibited better adsorption capability of Cu²⁺ and SDZ than the pristine biochar (BC). The corresponding maximum adsorption capacities of Fe-BC₇₀₀ were 46.85 mg g^-1 and 45.43 mg g^-1 towards Cu²⁺ and SDZ, respectively. Interestingly, the adsorption was elevated in binary-pollutants system, suggesting a synergistic effect, which was probably attributed to the mutual bridging effects and complexation between Cu²⁺ and SDZ. The loaded iron oxide particles could serve as a physical barrier to separate the adsorptions of Cu²⁺ and SDZ and thus inhibited the competitive adsorption. Meanwhile, theoretical calculation demonstrated that sulfonamide group was the most probable binding site. Columns packed with Fe-BC₇₀₀ showed better performances for Cu²⁺ and SDZ removal in binary system (635.73 BV for Cu²⁺ and 4846.26 BV for SDZ) than in single systems (571.60 BV for Cu²⁺ and 3572.06 BV for SDZ), which was consistent with batch adsorption experiments. These results demonstrated the potential application of Fe-BC₇₀₀ for simultaneous adsorption of Cu²⁺ and SDZ and provided a cost-effective way for the remediation of organic and inorganic pollutants.

Waste Tire Heat Treatment to Prepare Sulfur Self-Doped Char: Operando Insight into Activation Mechanisms Based on the Char Structures Evolution

Waste tire (WT) can be heat-treated to be high-quality sulfur self-doped char via pyrolysis and K2FeO4-assisted activation processes. This work aimed at further studying the activation mechanisms based on the char structures evolution by operando experimental method. Activation treatment process (from 50 °C to 800 °C and then held for 3 h) was divided into six typical stages (S1–S6) and consisted of carbonization process (S1–S4) and effective activation process (S4–S6). During the carbonization process, the specific capacitance only increased from 0.2 F/g to 12.4 F/g, aromatic ring systems and alkyl-aryl C-C bonds generated, S 2p3/2 (sulphide bridge) was mainly gradually consumed. During the effective activation process, the specific capacitance hugely increased from 12.4 F/g to 112.5 F/g, aromatic ring systems and alkyl-aryl C-C bonds turned to ordered graphitic char. The pores massively generated from S4 to S5, while micropores partly formed to larger and mesopores+macropores fractionally converting to smaller from S5 to S6. Besides, both S 2p3/2 and S 2p5/2 (sulphone bridge) were enriched after S5. Furthermore, the key structural parameters for huge improvement of specific capacitance were found and it further revealed that mesopores+macropores possessed stronger promotion effect than micropores and S 2p3/2 was more beneficial than S 2p5/2.