Sulfur-doped activated carbon for the efficient degradation of tetracycline with persulfate: Insight into the effect of pore structure on catalytic performance.

Sulfur-doped activated carbon has proved to be a promising metal-free catalyst for persulfate (PDS) catalytic activation for the oxidation of aqueous refractory organics. Herein, sulfur-doped porous carbon (ACS) catalysts with different pore structures and doped-S contents were prepared via a template method using d(+)-glucose as the carbon source, sulfur as the sulfur source, and nano-MgO with different particle sizes as templates. Characterization results showed that the particle size of MgO significantly affects the pore structure and doped-S content of ACSs catalysts: a sample synthesized with 20 nm MgO as template (ACS-20) presented the highest content of doped-S and a mesoporous structure, which endowed it with superior adsorption and catalytic performance toward tetracycline (TC) removal. The effect of catalyst dosage, TC concentration, PDS concentration and solution pH on TC removal efficiency were evaluated. The reaction mechanism, investigated by combination of EPR, quenching experiments and LC-MS, indicated that the reactive species included HO·, SO4˙-, and 1O2, but that 1O2 played the dominant role in TC oxidation through a non-radical oxidation pathway. In addition, the reusability and regeneration properties of the ACS-20 catalyst were also studied. This work provides a promising strategy and some theoretical basis for the design and preparation of activated carbon catalysts for advanced oxidation reactions from the viewpoint of pore structure design and S-doping.

Efficient charge separation in sulfur doped AgFeO2 photocatalyst for enhanced photocatalytic U(VI) reduction: The role of doping and mechanism insights.

Photocatalytic reduction of U(VI) in aqueous solutions has been considered as an efficient and promising technology to solve radioactive U pollution. In this work, density functional theory (DFT) calculations were firstly employed to optimize and compare the adsorption configurations combined uranium with four given photocatalysts, then their adsorption energies were - 0.97 eV for AgFeO2, - 1.15 eV for Zn doped AgFeO2, - 1.73 eV for Cu doped AgFeO2 and - 2.66 eV for S doped AgFeO2, respectively, indicating the sulfur doping plays a major role in U(VI) photoreduction. Herein, a visible light responsive efficient sulfur doped AgFeO2 photocatalyst (S doped AgFeO2) was synthesized and utilized to photocatalytic reduction of U(VI) in aqueous solutions. According to XRD, XPS and TEM analysis, the sulfur was successfully doped in AgFeO2 via the hydrothermal method. The batch experimental showed that S doping enhanced the U(VI) photoreduction activity of AgFeO2, and the S-AFO-3 photocatalyst exhibited the highest photocatalytic activity (92.57%), which was 1.5 times than that of pure AgFeO2. ESR, PL and DFT results demonstrated that the enhancement of adsorbed U(VI) photoreduction was attributed to the own unique effect of oxygen vacancy defects and efficient charge separation of S doped AgFeO2 photocatalyst. Due to its higher adsorption energies, fast-U(VI) photoreduction rate and superior chemical stability, the sulfur doped AgFeO2 photocatalyst is hoped for water remediation containing U(VI) wastewater.

Effect of activator/precursor mass ratio on sulfur-doped porous carbon for catalytic oxidation of aqueous organics with persulfate.

Sulfur-doped porous carbon has emerged as promising metal-free catalysts toward persulfate (PS) for catalytic oxidation of aqueous organics. Wherein, thermal pyrolysis with activator activation is very common for the preparation of activated carbon. However, the relationship between the mass ratio of activator/precursor and catalytic efficiency has been rarely reported. Herein, a series of sulfur-doped porous carbons (S-AC) were synthesized by one-step chemical activation of (Poly(phenylene sulphide) (PPS)) with K2CO3 as activator at K2CO3/PPS mass ratio ranging from 0 to 3. The effects of K2CO3/PPS mass ratio on its physicochemical properties and its catalytic performance for p-chlorophenol (PCP) degradation with PS were comprehensively investigated. Experiment results show that sulfur doping enhanced its catalytic activity and the sample synthesized with K2CO3/PPS mass ratio of 2 (S-AC-2) exhibited the best adsorption and catalytic performance toward PS for PCP removal. More importantly, S-AC-2 with PS could efficiently degrade various aqueous toxic organics other than PCP, and S-AC-2 showed superior catalytic activity to many recently reported advanced materials. In addition, the effects of several operate parameters, including reaction temperature, PS concentration, pH, humic acid, and inorganic ions on PCP oxidation were evaluated. By combining with the results of quenching experiments and EPR, the PS activation mechanism over S-AC-2 was revealed. Moreover, the reusability and regenerability of S-AC-2 was also studied. It indicates that S-AC-2 showed inferior reusability, but the catalytic activity of which could be fully recovered through thermal treatment at 600 °C for 2 h in N2.

Hydroxyapatite modified ZIF-67 composite with abundant binding groups for the highly efficient and selective elimination of uranium (VI) from wastewater.

In this work, nanoscale hydroxyapatite (HAP)-modified ZIF-67 composite, HAP/ZIF-67, with abundant functional groups for uranium(VI) binding was synthesized via a facile ultrasound-assisted synthesis method. The prepared HAP/ZIF-67 was characterized by XRD, SEM, TEM, BET, FT-IR and XPS techniques, and was applied to eliminate uranium(VI) from aqueous solutions under various conditions, i.e., pH, coexisting ions, temperature and contact time. The results indicate that the abundant Co-OH, -CN- and -NH- binding groups originating from the ZIF-67 and the Ca-OH and PO43- derived from loaded nanoscale HAP synergistically endowed HAP/ZIF-67 with the excellent U(VI) adsorption capacity of 453.1 mg/g, which is 2.55 and 1.78 times that of pristine HAP and ZIF-67. HAP/ZIF-67 showed high adsorption selectivity toward U(VI), and the U(VI) elimination efficiency for real wastewater by HAP/ZIF-67 reached 97.29%. The adsorption kinetics and isotherms were well simulated by the pseudo-second-order model and Langmuir isotherm model, respectively, suggesting that U(VI) adsorption was an endothermic monolayer chemisorption process. The adsorption mechanism of U (VI) by HAP/ZIF-67 was dominated by surface complexation process. This work is expected to provide an effective strategy for developing HAP-modified MOFs absorbent to be used for the highly efficient elimination of radionuclides from wastewater.

Synthesis of dimethyl carbonate from CO2 and methanol over a hydrophobic Ce/SBA-15 catalyst.

A series of Ce/SBA-15 catalysts with different degrees of hydrophobicities were prepared via a post-grafting method and used for the direct synthesis of dimethyl carbonate (DMC) from CO2 and methanol. The Ce/SBA-15-6 catalyst exhibited the highest DMC yield of 0.2%, which was close to the equilibrium value under the reaction conditions of 130 °C, 12 h and 12 MPa. The catalysts were characterized via XRD, BET, FT-IR, solid-state 29Si MAS NMR, CA, TEM, XPS and NH3/CO2-TPD; the results indicated that the hydrophobicity of the catalysts facilitated the creation of oxygen vacancies, which could act as Lewis acids to activate methanol. Higher amounts of moderate acid sites led to higher yields of DMC. In addition, the hydrophobicity of the catalysts could also reduce the adsorbed water on their surface and increase the DMC yield while shortening the reaction time.