Co3O4 nanocube-decorated nitrogen-doped carbon foam as an enhanced 3-dimensional hierarchical catalyst for activating Oxone to degrade sulfosalicylic acid

Boosting elimination of sunscreen, Tetrahydroxybenzophenone (BP-2), from water using monopersulfate activated by thorny NanoBox of Co@C prepared via the engineered etching strategy: A comparative and mechanistic investigation

As sunscreens, benzophenones (BPs), are regarded as emerging contaminants, most of studies are focused on removal of 2-hydroxy-4-methoxybenzophenone (BP-3), which, however, has been employed for protecting skin. Another major class of BPs, which is used to prevent UV-induce degradation in various products, is completely neglected. Thus, this present study aims to develop a useful advanced oxidation process (AOP) for the first time to eliminate such a class of BP sunscreens from contaminated water. Specifically, 2,2',4,4'-Tetrahydroxybenzophenone (BP-2) would be focused here as BP-2 is intensively used in perfumes, lipsticks, and plastics for preventing the UV-induced degradation. As monopersulfate (MPS)-based AOP is practical for degrading emerging contaminants, a facile nanostructured cobalt-based material is then developed for maximizing catalytic activities of MPS activation by immobilizing Co nanoparticles onto carbon substrates. In particular, ZIF-67 is employed as a template, followed by the etching and carbonization treatments to afford the thorny nanobox of Co@C (TNBCC) with the hollow-nanostructure. In comparison to the solid (non-hollow) nanocube of Co@C (NCCC) from the direct carbonization of ZIF-67, TNBCC possesses not only the excellent textural features, but also superior electrochemical properties and highly reactive surfaces, making TNBCC exhibit the significantly higher catalytic activity than NCCC as well as Co₃O₄ in activating MPS to degrade BP-2. Mechanisms of BP-2 degradation are also elucidated and ascribed to both radical and non-radical routes. These advantageous features make TNBCC a useful catalyst of activating MPS in BP-2 degradation.

Base-metal oxide semiconductor electrodes for PPCP degradation: Ti-doped α-Fe2O3 for sulfosalicylic acid oxidation as an example

Sulfosalicylic acid is a typical pharmaceutical and personal care product with high toxicity, environmental persistence, and low biodegradability. Electrochemical oxidation has been demonstrated to be a promising way for hazardous organics treatment, but it is severely limited by the high cost and resource shortage of electrode materials. Base-metal oxide semiconductor anodes have the merits of low cost, diversity, and tunable energy levels for charge transfer, and thus may be alternatives to the electrodes for wastewater treatment. Herein, we found that Ti-doped α-Fe₂O₃, as an example, could be efficient for sulfosalicylic acid oxidation, reaching comparable faraday efficiency of sulfosalicylic acid to that of the boron-doped diamond electrode. Ti-doped electrodes exhibited both higher removal rates and current efficiency compared to the undoped. This could be mainly ascribed to the enhanced charge transfer rate constant. Kinetic analysis shows that the apparent reaction order, in terms of sulfosalicylic acid in bulk solution, depended on applied potential and pollutant concentration. Mechanism study shows that the oxidation of sulfosalicylic acid was mainly through indirect pathway. Moreover, the oxidation products were determined and the oxidation mechanism was proposed. This study may open a door to employ base-metal oxide semiconductor anodes for the efficient treatment of organic wastewater.

Templating agent-mediated Cobalt oxide encapsulated in Mesoporous silica as an efficient oxone activator for elimination of toxic anionic azo dye in water: Mechanistic and DFT-assisted investigations

While Azorubin S (AZRS) is extensively used as a reddish anionic azo dye for textiles and an alimentary colorant in food, AZRS is mutagenic/carcinogenic, and it shall be removed from dye-containing wastewaters. In view of advantages of SO₄^•--related chemical oxidation technology, oxone (KHSO₅) would an ideal source of SO₄^•- for degrading AZRS, and heterogeneous Co₃O₄-based catalysts is required and shall be developed for activating oxone. Herein, a facile protocol is proposed for fabricating mesoporous silica (MS)-confined Co₃O₄ by a templating agent-mediated dry-grinding procedure. As the templating agent retained inside the ordered pores of MS (before calcination) would facilitate insertion and dispersion of Co ions into pores, the resulting Co₃O₄ nanoparticles (NPs) would be grown and confined within the pores of MS after calcination, affording Co@MS. On the contrary, another analogue, Co/MS, is also prepared using the similar protocol without the templating agent-mediated introduction of Co, but Co₃O₄ NPs seriously aggregate as clusters on MS. Therefore, Co@MS outperforms Co/MS for activating oxone to eliminate AZRS. Co@MS shows a noticeably lower activation energy of AZRS elimination than the existing catalysts, revealing its advantage over the reported catalysts. Moreover, the mechanistic investigation of AZRS elimination by Co@MS-activated oxone has been also elucidated for identifying the presence of SO₄^•‒, ^•OH, and ¹O₂ in AZRS degradation using scavengers, electron paramagnetic resonance spectroscopy, and semi-quantification. The AZRS decomposition pathway is also investigated and unveiled in details via the DFT calculation. These results validate that Co@MS appears as a superior catalyst of oxone activation for AZRS degradation.

Adsorptive removal of sulfosalicylic acid from aqueous medium by iron(III)-loaded magnetic chitosan/graphene oxide

In this study, an iron(III)-loaded magnetic chitosan/graphene oxide composite (Fe-MCG) was synthesized and applied for the adsorptive removal of sulfosalicylic acid (SSA) in aqueous solution. The results obtained from the application of various characterization techniques such as scanning electron microscopy (SEM), vibrating-sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS) prove the successful formation of the composite with enhanced microstructure and superparamagnetic properties. The adsorption capacity of Fe-MCG towards SSA via batch mode reaches up to 135 mg/g at 293 K. The adsorption of SSA onto Fe-MCG is driven by monolayer adsorption with the chemical and physical adsorption processes both playing active roles. The Langmuir isotherm and pseudo-second-order kinetic models were observed to best describe the equilibrium adsorption and kinetic processes, respectively. The values obtained for the associated thermodynamic parameters confirm that the adsorptive process is spontaneous, exothermic and entropy-increasing. The efficacy and reusability of the spent Fe-MCG was studied using 0.01 mol/L NaOH solution. The kinetic process for the desorption of SSA from Fe-MCG is well described by the pseudo-second-order kinetic model. Based on the experimental results and XPS analysis, the underlying mechanisms for the uptake of SSA onto Fe-MCG involve electrostatic forces, complexation, π-π stacking, and hydrogen bonding. Overall, the excellent features of Fe-MCG enhance its potential as an adsorbent for the sequestration of SSA in environmental media.

Excellent photocatalytic performances of Co3O4-AC nanocomposites for H2 production via wastewater splitting

Natural sunlight-driven photocatalytic hydrogen production from wastewater is one of the most desirable techniques that can realize future green energy technology. Herein, we report the synthesis and the characterization of the biomass activated carbon (AC)-decorated cobalt oxide (Co₃O₄) nanocomposites for solar-stimulated photocatalytic hydrogen production from sulphide wastewater. The Co₃O₄-AC nanocomposites were ultrasonically synthesized by using hydrothermally-grown spinel Co₃O₄ nanoflakes and biomass-derived AC nanoflakes. Co₃O₄-AC showed a nanobundle-like aggregated morphology, and exhibited a large specific surface area (~133 m²/g). Through utilizing Co₃O₄-AC as a photocatalyst for photocatalytic splitting of sulphide wastewater (0.2 M) under solar irradiance with 730 W/m², an enhanced H₂ production efficiency (~70 mL/h) was achieved owing to the synergic effects from 2-dimentionally configured Co₃O₄ and AC microstructures; i.e., large surface area of Co₃O₄ and high electrical conductivity of AC. These findings suggest the nanocomposites of Co₃O₄-AC to hold great promise for the green approach of photocatalytic wastewater splitting.