Degradation of polyacrylamide in an ultrasonic-Fenton-like process using an acid-modified coal fly ash catalyst

Recent advances in ultrasound-Fenton/Fenton-like technology for degradation of aqueous organic pollutants

Organic pollutants in water are a serious problem because of their widespread presence, harming the ecosystem and human health. Of the commonly used advanced oxidation processes, a hybrid of ultrasound and the Fenton/Fenton-like technology has received increasing attention in treatment of aqueous organic pollutants. This hybrid is effective in degradation of organic pollutants, but its application has not been summarised. Herein, first, the application and influencing factors of this hybrid technology for organic pollutants degradation are introduced. Second, the mechanism of its action is discussed. Third, the current challenges and future perspectives associated with this technology are proposed. This review provides valuable information regarding this technology, deepens the understanding of its mechanisms of organic pollutants degradation and provides a reference for its use in treatment of aquatic environments.

Magnetic Adsorbent Fe3O4/ZnO/LC for the Removal of Tetracycline and Congo Red from Aqueous Solution

Zeolitic imidazolate frameworks (ZIFs) can be used as an adsorbent to efficiently adsorb organic pollutants. However, ZIF nanoparticles are easy to form aggregates, hampering the effective and practical application in practical adsorption. In this study, the ZIF-8 was successfully loaded onto lignocellulose (LC) to further produce ZnO/LC by in situ growth method and hydrothermal treatment, and then Fe3O4 nanoparticles (Fe3O4 NPs) were loaded onto ZnO/LC to prepare magnetic Fe3O4/ZnO/LC adsorbent for removing tetracycline (TC) and congo red (CR) pollutants from aqueous solution. The adsorption properties of the adsorbent were systematically analyzed for different conditions, such as adsorbent dosage, solution pH, contact time, temperature and initial concentration. The experimental data were fitted using adsorption kinetic and isotherm models. The results showed that the pseudo-second-order model and Sips model were well fitted to the adsorption kinetic and adsorption isotherm, respectively. The adsorption capacities of TC and CR reached the maximum value of 383.4 mg/g and 409.1 mg/g in experimental conditions. The mechanism of the removal mainly includes electrostatic interaction, hydrogen bonding and π-π stacking. This novel adsorbent could be rapidly separated from the aqueous solution, suggesting its high potential to remove pollutants in wastewater.

Mechanism analysis of hydroxypropyl guar gum degradation in fracture flowback fluid by homogeneous sono-Fenton process

An effective hybrid system was applied as the first report for the successful treatment of key pollutants (hydroxypropyl guar gum, HPG) in fracturing flowback fluid, and the synergistic index of the hybrid system was 20.45. In this regard, chemical oxygen demand (COD) removal ratio was evaluated with various influencing operating factors including reaction time, H2O2 concentration, Fe2+ concentration, ultrasonic power, initial pH, and temperature. The optimal operating parameters by single-factor analysis method were: the pH of 3.0, the H2O2 concentration of 80 mM, the Fe2+ concentration of 5 mM, the ultrasonic power of 180 W, the ultrasonic frequency of 20-25 kHz, the temperature of 39 ℃, the reaction time of 30 min, and the COD removal rate reached 81.15 %, which was permissible to discharge surface water sources based on the environmental standards. A possible mechanism for HPG degradation and the generation of reactive species was proposed. Results of quenching tests showed that various impacts of the decomposition rate by addition of scavengers had followed the order of EDTA-2Na < BQ < t-BuOH, therefore OH radicals had a dominant role in destructing the HPG. Based on the kinetic study, it was concluded that Chan Kinetic Model was more appropriate to describe the degradation of HPG. Identification of intermediates by GC-MS showed that a wide range of recalcitrant compounds was removed and/or degraded into small molecular compounds effectively after treatment. Under the optimal conditions, the sono-Fenton system was used to treat the fracturing flowback fluid with the initial COD value of 675.21 mg/L, and the COD value decreased to 80.83 mg/L after 60 min treatment, which was in line with the marine sewage discharge standard. In conclusion, sono-Fenton system can be introduced as a successful advanced treatment process for the efficient remediation of fracture flowback fluid.

Concurrent elimination and stepwise recovery of Pb(II) and bisphenol A from water using β-cyclodextrin modified magnetic cellulose: adsorption performance and mechanism investigation

Coexistence of heavy metals and endocrine disrupting compounds in polluted water with competitive adsorption behavior necessitates design of tailored adsorbents. In this work, β-cyclodextrin modified magnetic rice husk-derived cellulose (β-CD@MRHC) which can provide independent functional sites for effectively binding the above two types of contaminants was synthesized and used for Pb(II) and BPA elimination in both unit and multivariate systems. Characterizations results confirmed successful β-CD grafting and Fe₃O₄ loading, and the β-CD@MRHC had excellent magnetic property for its effectively recovery from water, which was not affected by the adsorption of pollutants. The β-CD@MRHC possessed superior adsorption performance with maximal Pb(II)/BPA uptake of 266.2 or 412.8 mg/g, severally, and the adsorption equilibrium was fleetly reached in 30 and 7.5 min. Moreover, the β-CD@MRHC could accomplish synergetic Pb(II) and BPA elimination through averting their competitive behaviors owing to diverse capture mechanisms for Pb(II) (ion exchange, complexation and electrostatic attraction) and BPA (hydrogen bonding and host-guest inclusion). Furthermore, after three cycles of step-wise desorption, the binding of Pb(II) as well as BPA byβ-CD@MRHC dropped slightly in dualistic condition. In summary, β-CD@MRHC was a promising tailored adsorbent to practical application for simultaneously removing heavy metals and organic matters from wastewater with high-performance magnetic recovery.

One-pot synthesis of Ca-based magnetic hydrochar derived from consecutive hydrothermal and pyrolysis processing of bamboo for high-performance scavenging of Pb(Ⅱ) and tetracycline from water

Ca-based magnetic bamboo-derived hydrochar described as Ca-MBHC was synthesized by one-pot pyrolysis, and was applied to remediation of lead (Pb) and tetracycline (TC) polluted water. Characterizations not only attested the loading of CaCO₃ and Fe⁰ onto the hydrochar, but also demonstrated the magnetism of Ca-MBHC. Adsorption kinetic experiments showed that the Ca-MBHC could eliminate Pb(II) and TC during a wide range of pH, and appeared rapid uptake equilibrium within 240 and 60 min for Pb(II) and TC, severally. Adsorption isotherm experiments showed that the Ca-MBHC possessed highest adsorption of 475.58 mg/g concerning Pb(II), and heterogeneous uptake of 142.44 mg/g for TC. Furthermore, the Ca-MBHC could achieve Pb(II) binding owing to complexation, reduction, ion exchange and electrostatic attraction, whereas the TC uptake might be related to π-π stacking reciprocities, pore filling and hydrogen bonding. Overall, the Ca-MBHC could be viewed as an excellent adsorbent for scavenging Pb(II) and tetracycline from water.

Magnetic porous biochar with high specific surface area derived from microwave-assisted hydrothermal and pyrolysis treatments of water hyacinth for Cr(Ⅵ) and tetracycline adsorption from water

Magnetic porous water hyacinth-derived biochar (MPBC_MW3) was synthesized via two-step Microwave (MW)-assisted processes. Characterization results not only testified high specific surface area (2097.50 m²/g) of the MPBC_MW3 assisted by MW-assisted pyrolysis, but also revealed its favorable magnetism derived from MW-assisted hydrothermal process. The MPBC_MW3 possessed pH-dependent monolayer adsorption capacities of 202.61 and 202.62 mg/g for Cr(VI) and TC with quick attainments of uptake equilibrium within 150 and 200 min. Moreover, the Cr(VI) and TC uptake were substantially steady under the interference from multifarious co-existing ions with slight decline after three adsorption-desorption cycles. Furthermore, the MPBC_MW3 was demonstrated to achieve excellent Cr(VI) binding primarily through complexation, electrostatic interaction, reduction and ion exchange, while presenting outstanding TC removal via pore filling, π-π stacking, hydrogen bonding force, electrostatic interaction and complexation. All these findings suggested the MPBC_MW3 synthesized by MW-assisted processes as an excellent adsorbent for purification of Cr(VI) and TC-contaminated water.

Removal of Cd(Ⅱ) and anthracene from water by β-cyclodextrin functionalized magnetic hydrochar: Performance, mechanism and recovery

Magnetic hydrochar modified by β-cyclodextrin (β-CD) described as β-CD@MHC was successfully synthesized and applied to simultaneous removal of cadmium (Cd) and anthracene (ANT). Characterizations attested the grafting of β-CD groups onto β-CD@MHC with excellent magnetism. Moreover, the β-CD@MHC could eliminate Cd(II) and ANT during an extensive pH scope, and presented fast adsorption equilibrium in 60 min and 80 min for Cd(II) and ANT, respectively. And the β-CD@MHC possessed prominent adsorption properties with maximum monolayer binding of 47.28 mg/g for Cd(II), and corresponding heterogeneous uptake of 60.27 mg/g concerning ANT. Furthermore, the β-CD@MHC could effectively avoid the competitive behavior between Cd(II) and ANT mainly due to complexation and electrostatic attraction effects for capturing Cd(II), and host-guest interaction in the removal of ANT. Additionally, the binding of Cd(II) and ANT onto β-CD@MHC dropped slightly after stepwise desorption, suggesting the β-CD@MHC as a high-performance adsorbent for heavy metals and PAHs elimination from wastewater.

Green synthesis of hydrophilic activated carbon supported sulfide nZVI for enhanced Pb(II) scavenging from water: Characterization, kinetics, isotherms and mechanisms

For green synthesis of nZVI with low aggregation and high antioxidation, green tea extracts were explored as reductant during the synthesis with modification by hydrophilic porous activated carbon (HPAC) and sulfidation technology. Characterization results identified the effective preparation of porous activated carbon (PAC) with microporous and mesoporous characteristics, and the successful loading of S-nZVI nanoparticles on S-nZVI@HPAC. Moreover, HPAC was identified to have a higher degree of hydrophilicity surface compared to PAC, while the S-nZVI with an atomic ratio of S/Fe (0.16) further improved the hydrophilic performance of S-nZVI@HPAC. Batch adsorption revealed that the S-nZVI@HPAC possessed a pH-dependent adsorption performance with a fast kinetic equilibrium within 120 min and an outstanding Pb(II) binding of 295.30 mg/g at pH = 5.0 and 50 °C. Thermodynamic results exhibited positive ΔH° and ΔS°, clearly indicative of the endothermic property of Pb(II) uptake onto S-nZVI@HPAC with an increase in randomness, while the negative ΔG° uncovered a favorable and spontaneous process. Furthermore, the S-nZVI@HPAC was believed to enhance the Pb(II) uptake via the synergistic effects of electrostatic attraction, chemical precipitation, complexation and reduction. The results of this work highlighted the hydrophilic porous activated carbon supported sulfide nZVI for efficient remediation of Pb(II) contaminated water.