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Enhancing the degradation of ciprofloxacin in water using Oxone activated by urchin-like cubic and hollow-structured cobalt@N-doped carbon.

Single-atom catalysts have been believed as ideal materials for achieving maximum utilization of the metal active sites in Fenton-like catalysis for eliminating organic pollutants. However, the relationship between single-atom structure...

Polyaniline modified activated carbon shows outstanding capacitive deionization ability because of the synergism between electrical double layer adsorption and pseudocapacitive deionization.

Thiophene ring implanted two-dimensional carbon nitride nanosheets (2D Thing-CNNS) with dramatically double elevated n → π* electronic transitions were synthesized. 2D Thing-CNNS exhibited efficient photocatalytic bisphenol-A degradation.

Emerging single atom catalysts (SACs), especially carbon-based SACs are appealing materials in environmental catalysis because of their ultrahigh performances, environmental friendliness, structural/chemical robustness, and the maximum utilization of active metal sites. The metal centres, carbon matrixes, and coordination characteristics collectively determine the electronic features of carbon-based SACs, and their behaviours in catalysing peroxide activation and efficiencies in advanced oxidation processes (AOPs). However, there is lack of a comprehensive and critical review reporting the successful marriage of carbon-based SACs in AOP-based remediation technologies. It is particularly necessary to systematically compare and reveal the catalytic sites and the associated mechanisms of carbon-based SACs in diverse AOP systems. In this review, we highlight the synthetic strategies, characterisation, and computation of carbon-based SACs, and for the first time, showcase their innovative applications in AOP technologies. We unveil the origins of versatile catalytic oxidation pathways in different AOP systems and the mechanisms of micropollutant degradation over carbon-based SACs, distinguished from the upsized counterparts (metals/oxides and carbon substrates). We also provide directions to the rational design of on-demand SACs for green chemistry and environmental sustainability. Also, we suggest a designated and integrated experimental/theoretical protocol for revealing the structure-catalysis relations of SACs in AOP applications, and propose the prospects for future opportunities and challenges.

Natural mechanical energies, such as wind, tidal waves, and water flow, widely exist in the environment and these inexhaustible natural mechanical energies can be utilized through piezoelectric materials for the degradation of aqueous organic pollutants in the environment. In this work, few-layered molybdenum disulfide nanoflowers (MoS2 NFs) were adopted as a piezocatalyst to activate peroxymonosulfate (PMS) with ultrasonic waves (US) as the mechanical force for phenol abatement. A much higher degradation efficiency was attained by the integrated US/MoS2 NFs/PMS system compared to other single systems, revealing the markedly synergistic effect of US and MoS2 on PMS activation. Moreover, density functional theory calculations were performed to fundamentally understand the charge distribution in a polarized MoS2 nanosheet under different strains and to understand the piezocatalytic properties of MoS2 nanosheets, as well as reaction pathways between PMS and carriers on the active edges of MoS2 for the production of free radicals. It was found that both sulfate radicals (SO4˙−) and hydroxyl radicals (˙OH) were produced in the US/MoS2 NFs/PMS system. However, SO4˙− was quickly converted into ˙OH via a hydrolysis reaction under US, enabling ˙OH to be the primary reactive oxygen species for phenol oxidation. This work offers an efficient piezocatalyst to activate persulfate for water remediation. More importantly, it provides fundamental insights into the piezoelectricity in two-dimensional semiconducting materials and the mechanism in the piezocatalytic activation of persulfate. Results prove that the combination of piezoelectricity and advanced oxidation processes is promising for water pollution control, and provides a new idea for the application of inexhaustible natural mechanical energy in the environment for environmental remediation.

Perfluorooctanoic acid (PFOA, C7F15COOH) has raised global concerns because of its ubiquitous occurrence and resistance to most conventional water treatment techniques. In this work, we first used metal–organic framework (MOF) derived In2O3 nanospheres (In2O3 NS) and rods for photocatalytic degradation of PFOA under UV light irradiation. XRD was used to confirm the successful preparation of MOF-derived In2O3. SEM images show that In2O3 NS and rods were obtained by the calcination of different indium (III)–benzenedicarboxylate (In–BDC) MOFs. In2O3 NS and rods demonstrated enhanced performances for photodegradation of PFOA compared with the commercial In2O3. The results show that PFOA was completely decomposed in 3 h, and its shorter-chain products were further mineralized in 6 h in the presence of In2O3 NS under 254 nm UV light irradiation. MOF-derived In2O3 is super-hydrophilic with a contact angle of ∼20° and possesses larger specific surface area, which facilitate the adsorption and tight coordination of PFOA with In2O3. Moreover, EIS Nyquist spectra show that the as-prepared In2O3 NS and rods have higher efficiency in charge separation and migration compared with the commercial In2O3. All these properties contribute to the destruction of PFOA.

Carbon-based catalytic ozonation is state-of-the-art technology with high oxidation capabilities for wastewater remediation, taking advantage of the synergies of direct ozone oxidation and the generated reactive oxygen species (ROS). Replacing metal-based materials with active and robust carbonaceous catalysts in catalytic ozonation will lead to outperformed catalytic performance, minimized operational cost, and no secondary contamination. Additionally, the variety of allotropes and maneuverable surface chemistry of carbons facilitate structural and surface engineering, which enables the regulation of reactivity, stability and reaction pathways. This review summarizes the recent development of structural control and surface modification of carbocatalysts and their applications in catalytic ozonation. The structure–performance relations and mechanisms are elucidated by a novel model based on the interaction intensity between reactants and carbon surface. Meanwhile, influences of the water matrix parameters on the catalytic system are unveiled. Finally, we provide directions to the rational design of reaction-oriented carbocatalysts, the methodology for mechanistic explorations, and the implementation of ozone-based AOPs in real wastewater treatment.

Persulfate-based advanced oxidation processes are promising technologies to solve water pollution. In this work, single iron atoms are anchored on three-dimensional N-doped carbon nanosheets by a chemical vapor deposition (CVD) method with ferrocene-loaded CaO as the hard template. The high surface density of Fe–N4 sites and abundant interconnected meso–macro pores are highly favorable for activating peroxymonosulfate (PMS) to produce superoxide radicals (O2˙−), giving rise to ultrahigh activity and excellent stability for pollutant degradation. Experiment and density functional theory (DFT) calculations reveal that Fe–N4 is the main active site, on which electrons transfer from C to Fe via the C–N–Fe bond to secure the low-valence state of Fe species for the redox process. This work proposes a new strategy for developing highly active single-atom materials by CVD and reveals mechanisms of PMS activation on single-atom activators.

Manganese oxides, with low toxicity and wide adaptability, have been demonstrated as promising catalysts for substituting noble metals/oxides in a diversity of chemical reactions. In environmental remediation, manganese oxides can catalyze peroxides to produce reactive oxygen species (ROS) in an aqueous phase for in situ chemical oxidation (ISCO) and advanced oxidation processes (AOPs). The manganese oxides stand out among the transition metal oxides due to their inherent dissimilarity in redox properties, crystal structure, and surface nano-architectures. In this paper, a comprehensive review is presented on the formation of nanostructured manganese oxides in nature (abiotic oxidation and biogenic evolution) as well as their artificial synthesis with rationally controlled tunnels and layers, crystal structures, exposed facet orientations, dimensional architecture and oxidation states. We further overview the applications of nanostructured manganese oxides in activation of various peroxides for catalytic oxidation to destroy organic contaminants during water purification. The roles of manganese oxides are emphasized in catalytic activation of hydrogen peroxide (H2O2), ozone (O3), and persulfates (peroxymonosulfate and peroxydisulfate). The mechanisms of the interactions between manganese oxides with the diverse peroxides and structure-dependent ROS production will be illustrated. The regulating rules of compositional alien-metal doping, formation of mixed metal oxides and hybrid materials are further discussed regarding the promoted catalytic activity. More importantly, both radical oxidation and nonradical pathways involved in manganese-based AOPs will be illustrated. Lastly, we will propose several prospects for future development of manganese oxides in practical applications.

Carbon-catalyzed persulfate activation is a metal-free advanced oxidation process for abating aqueous organic micropollutants. Recently, the electron-transfer mechanism in the activation of peroxydisulfate (PDS) has attracted tremendous interest due to its unknown nonradical reaction pathways. The conventionally used atomic-scale descriptors of adsorption energy (Eads), O–O bond length (lO–O) and S–O bond length (lS–O) cannot accurately reflect the ability of the functionalities of PDS in its activation. In this work, a new descriptor, local electrophilicity index (ω), which represents the oxidative capacity of adsorbed S2O82−, was included to identify the intrinsic active sites in carbocatalysts via density functional theory calculations. To verify the reliability of the proposed criteria, the catalytic performances of a series of highly boronated and nitrogenated carbon nanotube/nanosheet composites (BCN-NT/NS) with tailored physicochemical properties were comparatively studied for activating PDS to degrade phenol. By integrating the computational and experimental results, the catalytic activity of BCN-NT/NS was determined to not only be related to the contents of heteroatom dopants (B and N), but also the positions of B and N in the co-doping configurations. This study offers reliable criteria for determining the intrinsic catalytic sites in carbocatalysts for the activation of PDS based on an electron-transfer mechanism, which assists the rational design of nanocarbons as advanced catalysts for metal-free oxidation and water remediation.

Catalysts containing both nanoclusters and single atom metal sites have received increasing attention because of their superior catalytic activities to their aggregated counterparts. Herein, ultrafine CuO nanoclusters along with Cu single atoms were anchored onto typical mesoporous silica SBA-15 for Fenton-like reactions, and the obtained catalysts were named UNCu-SBA. Both advanced characterization and computational studies offered convincing evidence for the unique structural feature. XPS and XANES identified the valence state of Cu(II) on UNCu-SBA. Fenton-like reactions further demonstrated that UNCu-SBA manifested higher activities in comparison with APCu-SBA, which contained aggregated CuO particles. Moreover, the Cu mass normalized rate constant of UNCu-SBA was 18 times larger than that of APCu-SBA, suggesting an exceptional Cu atom utility in UNCu-SBA. The UNCu-SBA catalyst was able to activate H2O2 to generate ˙OH in a wider pH range of 4–7 than in typical Fenton reactions (2–4). This may direct future advances toward AOP nanocatalysis.

3D graphene-based macrostructures have been recognized as promising candidates for adsorption and separation of water pollutants due to their well-defined porous structures and high surface areas. In this work, 3D graphene oxide hydrogel membranes (GOHMs) are fabricated by gelation of GO with ferrous ions via vacuum filtration. The ferrous ions serve as cross-linkers to increase the bonding strength between GO nanosheets and to induce microstructure transformation of GO via cation–π interactions to form a 3D lamellar porous structure. Compared with the pure GO membrane, GOHMs not only display high stability in water but also show considerably improved water permeability (111.5 L m−2 h−1 bar−1) and retention performances (>99%) for methylene blue (MB), because the hydrogel structure impressively enhances the connectivity of nanopores as well as the adsorption capacity. In addition, the nanostructures of GOHMs can be controlled by adjusting the amounts of GO or ferrous ions. The water permeation and MB retention reveal the structural changes of different GOHMs, which are consistent with the observations from scanning electron microscopy (SEM) and X-ray diffraction (XRD). Besides, GOHMs exhibit high permeation and separation performances in a wide pH range, and could effectively remove diverse organic contaminants by a facile filtration process via different separation mechanisms. Therefore, the GOHMs demonstrate a promising technique for practical wastewater purification.

Metal-free materials have exhibited great merits as substitutes for toxic and scarce metals/oxides in environmental catalysis. In this work, amorphous boron (A-Boron) is exploited as a nonmetal catalyst for peroxide activation. It is discovered that A-Boron is exclusively reactive for peroxymonosulfate (PMS) activation for the degradation of a diversity of organic contaminants in water, including benzenes, phenolics, dyes and antibiotics. Moreover, comparative tests show that A-Boron stands out among diverse heterogeneous catalysts, such as transition metal oxides, nanocarbons and non-carbonaceous materials (sulfur, phosphorus, boron nitride, and boron carbide). Competitive radical scavenging tests and in situ radical capture analysis by electron paramagnetic resonance (EPR) revealed that both sulfate (minor contribution) and hydroxyl radicals (dominant contribution) are generated and account for the organic oxidation. Advanced characterisation techniques suggest that the boron-based catalysis stems from the short-range ordered grain boundaries and amorphous domains in A-Boron. This is further evidenced by the fact that after thermal treatment, the surface-tailored boron samples (A-B-400 to 1000) exhibit inferior activities, with 10.4% to 28.3% phenol removal compared with A-Boron (74.3%); this is due to the formation of surface boric acid/hydroxide, which blocks the active boron phases. Theoretical calculations illustrate that the (1 0 0), (1 0 1) and (1 1 0) terminations and amorphous regions of elemental boron can directly cleave the peroxide O–O bond and decompose PMS to produce reactive hydroxyl radicals, which is in agreement with the experimental discoveries. This study provides a novel metal-free catalytic system for wastewater treatment and provides the first mechanistic insights into the origins of boron-based catalysis.

© The Royal Society of Chemistry 2019. Biomass is a naturally abundant, sustainable and clean resource, which has potential to replace a portion of the finite petroleum and fossil feedstock for sustainable production of value-added chemicals and fuels. However, an efficient conversion process is still difficult to be achieved due to the complex nature of biomass. Currently, the simple, mild, and environmentally benign photocatalytic process appears to be a new research avenue for lignocellulosic biomass transformation. This review provides insights into the state-of-the-art accomplishments in photocatalytic conversion of lignocellulosic biomass and its derivatives, including selective cleavage of dominant bonds of lignin, valorization of processed and native lignin, photoreforming reactions of cellulose and its intermediates, and the depolymerization of robust native lignocellulose under visible or UVA light irradiation. In addition, electricity production from photocatalytic conversion of biomass is also discussed as an innovative lignocellulosic biomass transformation process. We then put forward perspectives for photocatalytic conversion of native lignocellulose and future challenges in increasing the profitability and sustainability of a photocatalysis biorefinery system.

A route to rare spiro-3H-indazoles bearing a carbonyl group adjacent to the spirocyclic quarternary carbon via 1,3-dipolar cycloaddition reaction of arynes with 6-diazocyclohex-2-en-1-one derivatives under mild conditions has been developed. Further transformation of these unique spiro-3H-indazoles via an acid- or heat-mediated rearrangement to fused-2H-indazoles and an interesting reduction/ring-opening/reduction sequence are also described.

The synthesis of carbonaceous materials from a metal organic framework (MIL-100), organic linker and N-precursor was comprehensively investigated, and the structures of the products were characterized. It was found that simple pyrolysis of mixed MIL-100 (Fe)/dicyandiamide (DCDA) could produce nitrogen-doped graphene (N-graphene). The N-graphene showed excellent performances in peroxymonosulfate (PMS) activation, which were superior to those of counterparts of graphene, iron(II, III) oxide, manganese(IV) oxide and cobalt(II, III) oxide. With PMS activation, N-graphene exhibited efficient catalytic degradation of various organic pollutants such as phenol, 2,4,6-trichlorophenol (TCP), sulfachloropyridazine (SCP) and p-hydroxybenzoic acid (PHBA). Electron paramagnetic resonance (EPR) spectroscopy and radical quenching tests were employed to investigate the PMS activation and organic degradation processes. It was found that singlet oxygen (1O2) was mainly produced during the activation of PMS by N-graphene, and contributed to the catalytic oxidation instead of sulfate and/or hydroxyl radicals. These findings provide new insights into PMS activation by metal-free carbon catalysis.

Nitrogen-doped reduced graphene oxide (N-rGO) was prepared by a simple process of simultaneous reduction and nitrogen doping on graphene oxide (GO) at low temperatures using ammonium nitrate as a N precursor. Characterization techniques indicated that N-rGO materials with a high N loading (5–8 at%) can be easily produced and that the crystal/micro-structures and chemical compositions of N-rGO materials are dependent on the calcination conditions. The metal-free catalysis of N-rGO was investigated by catalytic activation of peroxymonosulfate (PMS) for phenol oxidative degradation in water. It was found that N-rGO samples are promising green catalysts for phenol degradation. Kinetic studies showed that phenol degradation follows first order reaction kinetics on N-rGO-350 with an activation energy of 31.6 kJ mol−1. The mechanism of PMS activation and phenol oxidation was elucidated by employing both electron paramagnetic resonance (EPR) studies and quenching tests with ethanol and tert-butanol.