Adsorption performance of tetracycline by the biomass ash derived from the pyrolysis of FeCl3-activated municipal sludge without gas protection.

The municipal sludge activated by FeCl3 solution was pyrolyzed at 500 °C without gas protection, and the pyrolysis products, named as biomass ash, could effectively adsorb tetracycline (TC) from aqueous solution. Different FeCl3 concentrations could directly affect the physicochemical properties of the biomass ash, so that the biomass ash as adsorbent showed different adsorption efficiency toward TC. The activation of FeCl3 increased the oxygen-containing functional groups and surface polarities of the biomass ash. When the concentration of FeCl3 solution was 0.5 mol/L, the biomass ash behaved the maximum specific surface area (37.74 m2/g) and the best adsorption efficiency. The pseudo-second-order kinetics model and the Freundlich multi-molecule model could fully explain the TC adsorption process by the biomass ash pyrolyzed from municipal sludge activated by FeCl3. Moreover, the adsorption mechanism was mainly attributed to the chemical adsorption.

Biomass ash pyrolyzed from municipal sludge and its adsorption performance toward tetracycline: effect of pyrolysis temperature and KOH activation.

Large amount of municipal sludge is difficult to handle; its resource utilization is an effective measure. In this study, the municipal sludge from sewage treatment plant was pyrolyzed without gas protection at different temperatures and potassium hydroxide (KOH) concentrations for activation. The pyrolysis products, named biomass ash, with higher surface area and enriched pore structures could be obtained at the pyrolysis temperature of 773 K. Moreover, the KOH activation for raw municipal sludge could further increase the surface area of the pyrolysis biomass ash. The maximum specific surface area was 44.71 m2/g, which was obtained under 2 mol/L KOH activation before pyrolysis at 773 K. And in this situation, the obtained pyrolysis biomass ash as adsorbent showed the maximum adsorption capacity of 50.75 mg/g toward tetracycline (TC). Moreover, the TC adsorption onto pyrolysis biomass ash obtained under various conditions followed the pseudo-second-order kinetic model. Adsorption thermodynamics analysis suggested the TC adsorption onto the pyrolysis biomass ash with no pre-activation was mainly due to the multi-molecule heterogeneous adsorption, while the TC adsorption onto pyrolysis biomass ash pretreated through the activation of KOH followed the monomer adsorption mechanism. This different adsorption mechanism was largely related to the pore structure, polarity, and aromaticity of the adsorbent.

Ag3PO4-based photocatalysts and their application in organic-polluted wastewater treatment.

Semiconductor photocatalysis technology has shown great potential in the field of organic pollutant removal, as it can use clean and pollution-free solar energy as driving force. The discovery of silver phosphate (Ag3PO4) is a major breakthrough in the field of visible light responsive semiconductor photocatalysis due to its robust capacity to absorb visible light < 520 nm. Furthermore, the holes produced in Ag3PO4 under light excitation possess a strong oxidation ability. However, the strong oxidation activity of Ag3PO4 is only achieved in the presence of electron sacrifice agents. Otherwise, photocorrosion would greatly reduce the reuse efficiency of Ag3PO4. This review thus focuses on the structural characteristics and preparation methods of Ag3PO4. Particularly, the recent advances in noble metal deposition, ion doping, and semiconductor coupling, as well as methods of magnetic composite modification for the improvement of catalytic activity and recycling efficiency of Ag3PO4-based catalysts, were also discussed, and all of these measures could enhance the catalytic performance of Ag3PO4 toward organic pollutants degradation. Additionally, some potential modification methods for Ag3PO4 were also proposed. This review thus provides insights into the advantages and disadvantages of the application of Ag3PO4 in the field of photocatalysis, clarifies the photocorrosion essence of Ag3PO4, and reveals the means to improve photocatalytic activity and stability of Ag3PO4. Furthermore, it provides a theoretical and methodological basis for studying Ag3PO4-based photocatalyst and also compiles valuable information regarding the photocatalytic treatment of organic polluted wastewater.

Novel visible-light-driven SrCoO3/Ag3PO4 heterojunction with enhanced photocatalytic performance for tetracycline degradation.

The semiconductor photocatalytic technology has been considerably studied due to its excellent catalytic performance in water pollution control. Herein, in this study, novel SrCoO3/Ag3PO4 composite materials with different SrCoO3 content were synthesized via a simple hydrothermal synthesis method. The characteristics of the as-prepared samples were detected through SEM/HRTEM, XRD, UV-vis DRS, PL, ESR, FT-IR, and XPS techniques, and then, the photocatalytic performance of SrCoO3/Ag3PO4 toward the degradation of tetracycline was investigated. When the mass ratio of SrCoO3 and Ag3PO4 in the composite was 1:1.5, the degradation rate constant of tetracycline in SrCoO3/Ag3PO4 (1:1.5) system is 0.0102 min-1, which is 1.7 times that of the Ag3PO4, and 3.78 times that of the SrCoO3. In addition, reactive species were also analyzed through the free radical trapping experiment and DMPO spin-trapping ESR spectra analysis, showing that OH•, h+, and O2•-participated in the catalytic degradation process of tetracycline to varying degrees. Finally, the photocatalytic mechanism of SrCoO3/Ag3PO4 was also proposed.

Photocatalytic performance and mechanism of Z-Scheme CuBi2O4/Ag3PO4 in the degradation of diclofenac sodium under visible light irradiation: Effects of pH, H2O2, and S2O82.

Highly efficient visible-light-responsive Z-Scheme CuBi2O4/Ag3PO4 photocatalysts were prepared by a hydrothermal synthesis and in-situ deposition method and characterized comprehensively. Under visible-light irradiation, the photocatalytic performance of CuBi2O4/Ag3PO4 in the degradation of diclofenac sodium (DS) in aqueous solutions was studied under different conditions such as different catalyst composition, solution pH, and concentration of S2O82- or H2O2, and the response surface methodology (RSM) was used to analyze the interaction effect of the parameters. The optimal activity of CuBi2O4/Ag3PO4 was achieved at the mass ratio of 3:7 and pH of 4.42. Moreover, the introduced S2O82- could significantly enhance the catalytic activity of CuBi2O4/Ag3PO4; when 1 mM S2O82- was added to the catalytic system, 10 mg/L of DS could be completely degraded within 60 min, but the structure of CuBi2O4/Ag3PO4 was severely destroyed. While when H2O2 was introduced into the system, both the activity and stability of CuBi2O4/Ag3PO4 were improved significantly. Finally, the photodegradation pathway of DS is proposed and the photocatalytic mechanism of CuBi2O4/Ag3PO4 under different conditions is explained. CuBi2O4/Ag3PO4 and CuBi2O4/Ag3PO4 (S2O82-) photocatalytic systems follow the Z-Scheme theory, and Ag0 formed on the surface of catalyst serves as the recombination center for the photogenerated e- from the conduction band (CB) of Ag3PO4 and h+ from the valence band (VB) of CuBi2O4; meanwhile, the catalytic degradation of DS by CuBi2O4/Ag3PO4 in the presence of H2O2 follows the heterojunction energy band theory.

Ag3PO4 Deposited on CuBi2O4 to Construct Z-Scheme Photocatalyst with Excellent Visible-Light Catalytic Performance Toward the Degradation of Diclofenac Sodium.

CuBi2O4/Ag3PO4 was synthesized through a combination of hydrothermal synthesis and an in situ deposition method with sodium stearate as additives, and their textures were characterized with XRD, XPS, SEM/HRTEM, EDS, UV-Vis, and PL. Then, the photodegradation performance of CuBi2O4/Ag3PO4 toward the degradation of diclofenac sodium (DS) was investigated, and the results indicate that the degradation rate of DS in a CuBi2O4/Ag3PO4 (1:1) system is 0.0143 min-1, which is 3.6 times that in the blank irradiation system. Finally, the photocatalytic mechanism of CuBi2O4/Ag3PO4 was discussed, which follows the Z-Scheme theory, and the performance enhancement of CuBi2O4/Ag3PO4 was attributed to the improved separation efficiency of photogenerated electron-hole pairs.