Direct transformation of bulk cobalt foam into cobalt nanoparticles encapsulated in nitrogen-doped carbon nanotubes for peroxymonosulfate activation toward rhodamine B degradation

N,S,O triply-doped carbon with nanotubes-interwoven nanosheets encapsulated Co nanoparticles for robust antibiotic destruction via activating peroxymonosulfate

The development of facile and effective approaches to regulate the stability and reusability of metallic Co catalytic materials towards peroxymonosulfate (PMS) activation for remediating antibiotic pollutants remains challenging. In this study, we develop a one-step pyrolysis strategy to fabricate three-dimensional porous architecture assembled with N,S,O-codoped carbon nanotube-interwoven hierarchically porous carbon nanosheets encapsulated Co nanoparticles (Co@NSOC), which serve as chainmail catalysts for stable and reusable degradation of tetracycline hydrochloride (TCH) through PMS activation. The optimal Co@NSOC-700-activated PMS system presents an excellent removal efficiency of 94.1 % for TCH within 10 min and a high cycling efficiency of 92.9 % after eight cycles. The encapsulated structure, abundant catalytic sites, superior hydrophilicity and strong magnetism contribute to the high performance. Further investigation demonstrates that both radical and nonradical pathways contribute to the TCH destruction, and 1O2 is verified as the dominant reactive substance. The possible degradation pathways and the toxicity of intermediates for TCH are evaluated. This work offers an innovative structure design and surface modulation strategy to fabricate robust catalysts towards environmental remediation.

Generation and identification of 1O2 in catalysts/peroxymonosulfate systems for water purification

Catalysts for peroxymonosulfate (PMS) activation are appealing in the purification of organic wastewater. Singlet oxygen (1O2) is widely recognized as a crucial reactive species for degrading organic contaminants in catalysts/PMS systems due to its adamant resistance to inorganic anions, high selectivity, and broad pH applicability. With the rapid growth of studies on 1O2 in catalysts/PMS systems, it becomes necessary to provide a comprehensive review of its current state. This review highlights recent advancements concerning 1O2 in catalysts/PMS systems, with a primary focus on generation pathways and identification methods. The generation pathways of 1O2 are summarized based on whether (distinguished by the geometric structures of metal species) or not (distinguished by the active sites) the metal element is included in the catalysts. Furthermore, this review thoroughly discusses the influence of metal valence states and metal species with different geometric structures on 1O2 generation. Various potential strategies are explored to regulate the generation of 1O2 from the perspective of catalyst design. Identification methods of 1O2 primarily include electron paramagnetic resonance (EPR), quenching experiments, reaction in D2O solution, and chemical probe tests in catalysts/PMS systems. The principles and applications of these methods are presented comprehensively along with their applicability, possible disagreements, and corresponding solutions. Besides, an identifying procedure on the combination of main identification methods is provided to evaluate the role of 1O2 in catalysts/PMS systems. Lastly, several perspectives for further studies are proposed to facilitate developments of 1O2 in catalysts/PMS systems.

Bifunctional Solar Evaporator with Co/N-Doped Graphene Oxide for Synergistic Steam Generation and Organic Pollutant Degradation

Solar-driven interfacial steam generation (SISG) is a promising technology for alleviating freshwater shortage. However, when the SISG technology is applied to wastewater treatment, the contaminant would be enriched in residual bulk water. Herein, a dual-functional evaporator was constructed via tactfully decorating Co/N-doped graphene oxide (GO) on melamine foam (MF), which can simultaneously achieve efficient vapor production and source water purification. N-doped carbon nanotubes (NCNTs) endowed evaporators with powerful light absorption and water transport performance, guaranteeing an evaporation rate of 2.02 kg m-2 h-1 under 1 sun irradiation. Meanwhile, the catalytic activity of the carbon layer was adjusted by the N dopant and embedded Co particles, providing abundant active sites to activate peroxymonosulfate (PMS). When treating the solution containing sulfamethoxazole (SMX), no SMX residues were detected in the remaining bulk water (up to 100% SMX degradation efficiency within 60 min), demonstrating that reactive oxygen species (ROS) were generated to attack SMX in the source water. The bifunctional evaporator successfully combined SISG and advanced oxidation processes (AOPs), providing an ingenious strategy for solving the problem of wastewater enrichment during SISG.

Applications of Carbon-Based Materials in Activated Peroxymonosulfate for the Degradation of Organic Pollutants: A Review

In recent years, water pollution has posed a serious threat to aquatic organisms and humans. Advanced oxidation processes (AOPs) based on activated peroxymonosulfate (PMS) show high oxidation, good selectivity, wide pH range and no secondary pollution in the removal of organic pollutants in water. Carbon-based materials are emerging green catalysts that can effectively activate persulfates to generate radical and non-radical active species to degrade organic pollutants. Compared with transition metal catalysts, carbon-based materials are widely used in SR-AOPs because of their low cost, non-toxicity, acid and alkali resistance, large specific surface area, and scalable surface charge, which can be used for selective control of specific water pollutants. This paper mainly presents several carbon-based materials used to activate PMS, including raw carbon materials and modified carbon materials (heteroatom-doped and metal-doped), analyzes and summarizes the mechanism of activating PMS by carbon-based catalysts, and discusses the influencing factors (temperature, pH, PMS concentration, catalyst concentration, inorganic anions, inorganic cations and dissolved oxygen) in the activation process. Finally, the future challenges and prospects of carbon-based materials in water pollution control are also presented.

Rhodamine B dye degradation using used face masks-derived carbon coupled with peroxymonosulfate

Catalytic carbon materials from used face masks (UFM) activated by peroxymonosulfate (PMS) were developed for the degradation of rhodamine B (RhB) dye in aqueous solution. The UFM-derived carbon (UFMC) catalyst had a relatively large surface area as well as active functional groups and promoted the generation of singlet ¹O₂ and radicals from PMS, giving a high RhB degradation performance (98.1% after 3 h) in the presence of 3 mM PMS. The UFMC could degrade only 13.7% at a minimal RhB dose of 10^-5 M. The principal reactive oxygen species of sulphate (SO₄^•), hydroxyl radicals (^•OH), and singlet ¹O₂ were discovered using electron paramagnetic resonance and radical scavenger studies. Finally, a toxicological plant and bacterial study was performed to demonstrate the potential non-toxicity of the degraded RhB water sample.

Rapid removal of high-concentration Rhodamine B by peroxymonosulfate activated with Co3O4-Fe3O4 composite loaded on rice straw biochar

In this study, rice straw biochar modified with Co₃O₄-Fe₃O₄ (RSBC@Co₃O₄-Fe₃O₄) was successfully prepared via calcinating oxalate coprecipitation precursor and employed as a catalyst to activate peroxymonosulfate (PMS) for the treatment of Rhodamine B (RhB)-simulated wastewater. The results indicated that RSBC@Co₃O₄-Fe₃O₄ exhibited high catalytic performance due to the synergy between Co₃O₄ and Fe₃O₄ doping into RSBC. Approximately 98% of RhB (180 mg/L) was degraded in the RSBC@Co₃O₄-Fe₃O₄/PMS system at initial pH 7 within 15 min. The degradation efficiency of RhB maintained over 90% after the fourth cycle, illustrating that RSBC@Co₃O₄-Fe₃O₄ displayed excellent stability and reusability. The primary reactive oxygen species (ROS) answerable for the degradation of RhB were ¹O₂, •OH, and SO₄^•-. Moreover, the intermediates involved in the degradation of RhB were identified and the possible degradation pathways were deduced. This work can provide a new approach to explore Co-based and BC-based catalysts for the degradation of organic pollutants.

Degradation of Textile Dye by Bimetallic Oxide Activated Peroxymonosulphate Process

The sulphate radical based advanced oxidation processes (AOPs) are highly in demand these days, owing to their numerous advantages. Herein, the Fe-Mn bimetallic oxide particle was used to activate peroxymonosulphate (PMS) for Rhodamine B (RhB) degradation. Three bimetallic catalysts were synthesized via the chemical precipitation method with different concentrations of metals; Fe-Mn (1:1), Fe-Mn (1:2) and Fe-Mn (2:1). The best performance was shown by Fe-Mn (2:1) system at optimized conditions; 96% of RhB was removed at optimized conditions. Scavenging experiments displayed the clear dominance of hydroxyl radical in pH 3, while sulphate radical was present in a large amount at pH 7 and 10. The monometallic Fe and Mn oxides were also synthesized to confirm the synergistic effect that was present in the bimetallic oxide system. The application of optimized condition in real textile wastewater was conducted, which revealed the system works efficiently at high concentrations of PMS and catalyst dosage.

Covalent organic frameworks@ZIF-67 derived novel nanocomposite catalyst effectively activated peroxymonosulfate to degrade organic pollutants

Metal organic frameworks-Covalent organic frameworks (MOFs-COFs) nanocomposites could improve the catalytic performance. Herein, a novel nanocomposite catalyst (CC@Co₃O₄) derived from MOFs-COFs (COF@ZIF-67) was prepared on peroxymonosulfate (PMS) activation for bisphenol A (BPA) and rhodamine B (RhB) degradation. Owing to the Co species, oxygen vacancy (O_V), surface hydroxyl (-OH), graphite N and ketone groups (C=O), the CC@Co₃O₄ exhibited higher catalytic degradation performance and total organic carbon (TOC) for BPA (93.8% and 22.3%) and RhB (98.2% and 82.5%) with a small quantity of catalyst (0.10 g/L) and low concentration of PMS (0.20 g/L) even without pH adjustment. Sulfate radicals (•SO₄^-), hydroxyl radicals (•OH), single oxygen (¹O₂), superoxide radicals (•O₂^-) and electron transfer process were all involved in the degradation of BPA and RhB. Among them, the degradation of BPA and RhB mainly depended on •O₂^- and ¹O₂, respectively. Meanwhile, the degradation pathways of BPA and RhB were proposed, and the biotoxicity of the degradation products was evaluated by freshwater chlorella. The results illustrated that the degradation products were environmentally friendly to organisms. In addition, the role of COF in the nanocomposites was also studied. The addition of COF remarkably improved the catalytic performance of CC@Co₃O₄ due to the faster electron transfer, more graphite N and C=O. Overall, this work may open the door to the development of COF-based catalysts in the field of water pollutant remediation.

Highly efficient activation of peroxymonosulfate by biomass juncus derived carbon decorated with cobalt nanoparticles for the degradation of ofloxacin

The cobalt nanoparticles decorated biomass Juncus derived carbon (Co@JDC) was prepared by facile calcination strategy and applied to activate peroxymonosulfate (PMS) for eliminating ofloxacin (OFX) in the water environment. The results of catalytic experiments show that 97% of OFX degradation efficiency and 70.4% of chemical oxygen demand removal rate are obtained within 24 min at 0.1 g L^-1 Co@JDC, 0.2 g L^-1 PMS, 20 mg L^-1 OFX (100 mL), and pH = 7, which indicates that Co@JDC/PMS system exhibits excellent performance. Meanwhile, the experimental results of affect factor show that Co@JDC/PMS system can operate in a wider pH range (3-9) and Cl^-1, NO₃^-1, and SO₄^2- have an ignorable effect on OFX degradation. The radical identification experiments confirm that SO₄˙^-, ·OH, O₂˙^-, and ¹O₂ are involved in the process of PMS activation, especially SO₄˙^- and ¹O₂ are the main contributors. Furthermore, a possible PMS activation mechanism by Co@JDC was proposed and the degradation pathways of OFX were deduced. Finally, the stable catalytic activity, negligible leaching of Co²⁺, and the outstanding degradation efficiency for other antibiotics prove that Co@JDC possesses good stability and universality.

Electronic structure modulation of multi-walled carbon nanotubes using azo dye for inducing non-radical reaction: Effect of graphitic nitrogen and structural defect

Multiwalled carbon nanotube (MWCNT) have a great potential for advanced oxidation process as a metal free catalyst. However, there catalytic activity is very low and needs to be appropriately tuned. Herein, we demonstrate a novel synthesis method for tuning the defect and surface functionality of MWCNT using azo dyes and the catalytic performance was tested for the degradation of different organic contaminates using PMS as an oxidant. The content, type of heteroatom functional groups, and the defect parameters were optimized by varying the pH and concentration of the organic dye. The quenching effect showed that singlet oxygen (¹O₂) is the primary reactive species generated by graphitic nitrogen, which can be boosted by the degree of graphitic structure disruption in MWCNT. The Linear sweep voltammetry (LSV) also confirmed that extrinsic doping enhanced the non-radical degradation by increasing the direct charge transfer rate from MB to PMS. Moreover, the designed catalyst showed a fast degradation performance with 35.1 kJ/mol activation energy and achieved the highest dye degradation rate and even surpassed some state-of-the-art metal-based and metal-free catalysts. The effect of inorganic anions study has also confirmed its industrial applicability.

Facile fabrication of surface vulcanized Co-Fe spinel oxide nanoparticles toward efficient 4-nitrophenol destruction

Developing efficient modulation strategies to boost the degradation efficiencies of non-noble metal catalysts for toxic phenolic compounds involving peroxymonosulfate (PMS)-based oxidation processes is essential but remains an arduous challenge. This study reports the one-pot construction of in-situ surface vulcanized CoFe₂O₄ @carbon (S_x-CF@C) to boost the PMS activation for 4-nitrophenol (4-NP) destruction. The direct pyrolysis of an aerogel precursor consisted of cobalt nitrate, ferric nitrate, melamine, and thiourea enables the as-formed S_x-CF@C with hierarchical structure, rich oxygen vacancies, and electron/mass transfer, thereby considerably promoting PMS activation performance of S_x-CF@C toward 4-NP degradation. Specifically, the optimal S_0.2-CF@C can achieve a removal efficiency of 99% for 4-NP destruction (20 mg/L) through PMS activation. Meanwhile, the catalyst also has generality to degrade a variety of antibiotic and dye organic pollutants. The radical quenching and electron paramagnetic resonance tests reveal the radical and non-radical activation mechanism in the S_0.2-CF@C/PMS system. The degradation pathway for 4-NP destruction over the S_0.2-CF@C/PMS system is proposed. This study provides an efficient approach to modulate the PMS activation performance of ferrite spinel materials toward the degradation of acute phenolic compounds.

Alkaline ultrasonic irradiation-mediated boosted H2 production over O/N-rich porous carbon anchored Ru nanoclusters

Developing efficient catalytic systems to boost hydrogen evolution from hydrolytic dehydrogenation of ammonia borane (AB) is of broad interest but remains a formidable challenge since the widespread usages of hydrogen have been considered as sustainable solutions to ensure future energy security. Herein, we developed an alkaline ultrasonic irradiation-mediated catalytic system with O/N-rich porous carbon supported Ru nanoclusters (NCs) (Ru/ONPC) to considerably boost the catalytic activity for hydrogen production from the hydrolytic dehydrogenation of AB. The uniformly distributed sub-2.0 nm Ru NCs on the ONPC were demonstrated to be efficient catalysts to boost hydrogen generation from the hydrolytic dehydrogenation of AB with the synergistic effect between ultrasonic irradiation and alkaline additive without any additional heating. An ultrahigh turnover frequency (TOF) of 4004 min^-1 was achieved in the developed catalytic system, which was significantly higher than that of ultrasound-mediated AB hydrolysis without alkali (TOF: 485 min^-1) and alkaline AB hydrolysis (TOF: 1747 min^-1) without ultrasound mixing. The alkaline ultrasonic irradiation was beneficial for the cleavage of the OH bonds in the attacked H₂O molecules catalyzed by the Ru/ONPC and thus considerably boost the catalytic hydrogen generation from AB. This study provides a tractable and ecofriendly pathway to promote the activity toward AB hydrolysis to release hydrogen.

Synergistic catalytic hydrolysis of ammonia borane to release hydrogen over AgCo@CN

Synergistic catalytic AB hydrolysis to generate hydrogen was achieved over AgCo@CN synthesized by auto-reduction between Co@CN and a Ag precursor.