Efficient purification of tetracycline wastewater by activated persulfate with heterogeneous Co-V bimetallic oxides

Comparative study of peroxymonosulfate activation with H2O2 activation by Cu-N doped biochar derived from peach gum network for rapid antibiotic removal

The design and development of efficient biochar catalysts is an urgent need for the removal of toxic contaminants from water bodies. Peach gum (PG) is a natural colloid featuring a heteropolysaccharide macromolecule structure. Herein, Cu2+ was anchored to the macromolecule of peach gum with dicyandiamide serving as the auxiliary ligand. Then, copper-nitrogen codoped peach gum biochar (Cu-N-PGC) was successfully prepared by the pyrolysis of the Cu2+/dicyandiamide modified peach gum precursor. Structural characterization demonstrated that CuO nanoparticles, pyridinic-N, and pyrrolic-N structures have been successfully constructed and uniformly doped into the graphitic structure of peach gum biochar. The mesoporous structure was fabricated in Cu-N-PGC composites by using NH4HCO3 as pore-making agent, and the adsorption of tetracycline (TC) on Cu-N-PGC-350 could be described by Langmuir isotherm model and pseudo-second-order kinetic model. The Cu-N-PGC biochar exhibited outstanding activation performance for peroxymonosulfate (PMS) and hydrogen peroxide (H2O2) in the removal of TC. Cu-N-PGC-350 showed the highest catalytic activity by activating PMS in the darkness, achieving a removal efficiency of 99.8 % for TC within 15 min. The rate constant obtained by PMS activation (0.38 min-1) was 4.47 times higher than that by H2O2 activation (0.085 min-1), suggesting Cu-N-PGC-350/PMS system was more efficient than the Cu-N-PGC-350/H2O2 system. The catalytic mechanism was studied through trapping experiments, EPR tests, and molecular electrostatic potential calculation, which reveals that 1O2 and SO4·- are the primary reactive species in the Cu-N-PGC-350/PMS system, while •OH is the main reactive radical generated in the Cu-N-PGC-350/H2O2 system. The degradation pathways of TC were proposed through the analysis of liquid chromatography-mass spectrometry (LC-MS), and the ecotoxicology of TC before and after degradation was evaluated by the TEST toxicity assessment and the rice seeds germination tests. This work presents an effective approach for the preparation of functional biochar with tree gum, thereby technically addressing the issue of uneven doping of metal-N active sites in biochar.

Eu3+-functionalized covalent organic framework for ratiometric fluorescence detection and adsorption of tetracycline and information steganography

Functional materials with organic/inorganic composites as the main matrix and rare earth ion complexes as the guest have shown a very broad application prospect for antibiotic sensors. However, Eu3+-complex often relies on a single fluorescence response signal, which is susceptible to changes in the detection environment and cannot simultaneously detect and remove tetracycline (TC). Herein, green fluorescent covalent two-dimensional organic framework (COF-TD) is synthesized, followed by modification of Eu3+ to synthesize COF-TD@Eu3+. In the ratiometric sensor, Eu3+ serves as the recognition site and specific response probe for TC, while COF-TD is the fluorescence reference and carrier for Eu3+. Due to the antenna effect, TC enhances the red fluorescence of Eu3+, while the green fluorescence of COF-TD remains almost stable. Based on the change of fluorescence intensity and fluorescence color from green to red, the efficient ratiometric sensing can be finished in 1 min. The developed method shows high sensitivity with a detection limit of 0.3 μM and high selectivity to TC which makes the method applicable to detect TC in traditional Chinese medicine preparations. In addition, due to the high specific surface area of COFs and specific adsorption sites, COF-TD@Eu3+ also shows good performance for TC removal. The findings show that the maximum adsorption capacity is 137.3 mg g-1 and the adsorption equilibrium is reached in 30 min. Smartphone assisted COF-TD@Eu3+ for both ratiometric fluorescence detection and detecting the absorption of TC is proposed for the first time. The molecular cryptosteganography that transforms the selective response of COF-TD@Eu3+ to binary strings is anticipated to advance utilization of nanomaterials in logic sensing and information safety.

Design of Environmental-Friendly Carbon-Based Catalysts for Efficient Advanced Oxidation Processes

Advanced oxidation processes (AOPs) represent one of the most promising strategies to generate highly reactive species to deal with organic dye-contaminated water. However, developing green and cost-effective catalysts is still a long-term goal for the wide practical application of AOPs. Herein, we demonstrated doping cobalt in porous carbon to efficiently catalyze the oxidation of the typically persistent organic pollutant rhodamine B, via multiple reactive species through the activation of peroxymonosulfate (PMS). The catalysts were prepared by facile pyrolysis of nanocomposites with a core of cobalt-loaded silica and a shell of phenolic resin (Co-C/SiO2). It showed that the produced 1O2 could effectively attack the electron-rich functional groups in rhodamine B, promoting its molecular chain breakage and accelerating its oxidative degradation reaction with reactive oxygen-containing radicals. The optimized Co-C/SiO2 catalyst exhibits impressive catalytic performance, with a degradation rate of rhodamine B up to 96.7% in 14 min and a reaction rate constant (k) as high as 0.2271 min-1, which suggested promising potential for its practical application.

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.

Investigation on water defluoridation via batch and continuous mode using Ce-Al bimetallic oxide: Adsorption dynamics, electrochemical and LCA analysis

With variable atomic ratios, Ce-Al bimetallic oxides were fabricated using the sol-gel combustion method and utilized for efficient fluoride removal. The synthesized bimetallic oxides were extensively studied using advanced characterization techniques, including TGA, XRD, FTIR, BET surface area analysis, EDX-assisted FESEM, XPS and impedance analysis. These techniques facilitate the interpretation of the chemical and physical properties of the synthesized material. The Ce-Al (1:1) bimetallic oxide was selected as an adsorbent for the defluoridation. The Ce-Al (1:1) oxide demonstrates a moderately high surface area of 108.67 m²/g. The sorption behaviour of fluoride on Ce-Al (1:1) was thoroughly investigated using batch and column modes. The maximum fluoride removal efficiency (99.4%) was achieved at a temperature of 45 °C and pH of 7.0 using an adsorbent dose of 0.18 g/L for 35 min. Pseudo-second-order kinetic model appropriately describes the sorption process. Freundlich's adsorption isotherm was more pertinent in representing fluoride adsorption behaviour. The maximum fluoride adsorption capacity is 146.73 mg/g at 45 °C. Thermodynamics study indicates fluoride adsorption on Ce-Al (1:1) bimetallic oxide is spontaneous and feasible. The adsorption mechanism was interpreted through XPS spectra, indicating that the physisorption process is mainly responsible for fluoride adsorption. An in-depth investigation of the adsorption dynamics was carried out using mass transfer models and found that the external diffusion process limits the overall adsorption rate. An electrochemical investigation was performed to understand the effect of fluoride adsorption on the electrochemical behaviour of bimetallic oxide. The fixed-bed column adsorption study suggested that the lower flow rate and increased bed height favourably impacted the overall defluoridation process, and column adsorption results were suitably interpreted through both the Adam-Bohart model and Yoon-Nelson dynamics model. The sustainable aspect of the defluoridation process was elucidated in terms of carbon footprint measurement using life cycle assessment analysis. The carbon footprint of the entire treatment process was calculated as 0.094 tons/year.

Heterogeneous Metal-Activated Persulfate and Electrochemically Activated Persulfate: A Review

The problem of organic pollution in wastewater is an important challenge due to its negative impact on the aquatic environment and human health. This review provides an outline of the research status for a sulfate-based advanced oxidation process in the removal of organic pollutants from water. The progress for metal catalyst activation and electrochemical activation is summarized including the use of catalyst-activated peroxymonosulfate (PMS) and peroxydisulfate (PDS) to generate hydroxyl radicals and sulfate radicals to degrade pollutants in water. This review covers mainly single metal (e.g., cobalt, copper, iron and manganese) and mixed metal catalyst activation as well as electrochemical activation in recent years. The leaching of metal ions in transition metal catalysts, the application of mixed metals, and the combination with the electrochemical process are summarized. The research and development process of the electrochemical activation process for the degradation of the main pollutants is also described in detail.