Anisotropic CoFe2O4@Graphene Hybrid Aerogels with High Flux and Excellent Stability as Building Blocks for Rapid Catalytic Degradation of Organic Contaminants in a Flow-Type Setup

Highly Aligned Graphene Aerogels for Multifunctional Composites

Stemming from the unique in-plane honeycomb lattice structure and the sp2 hybridized carbon atoms bonded by exceptionally strong carbon-carbon bonds, graphene exhibits remarkable anisotropic electrical, mechanical, and thermal properties. To maximize the utilization of graphene's in-plane properties, pre-constructed and aligned structures, such as oriented aerogels, films, and fibers, have been designed. The unique combination of aligned structure, high surface area, excellent electrical conductivity, mechanical stability, thermal conductivity, and porous nature of highly aligned graphene aerogels allows for tailored and enhanced performance in specific directions, enabling advancements in diverse fields. This review provides a comprehensive overview of recent advances in highly aligned graphene aerogels and their composites. It highlights the fabrication methods of aligned graphene aerogels and the optimization of alignment which can be estimated both qualitatively and quantitatively. The oriented scaffolds endow graphene aerogels and their composites with anisotropic properties, showing enhanced electrical, mechanical, and thermal properties along the alignment at the sacrifice of the perpendicular direction. This review showcases remarkable properties and applications of aligned graphene aerogels and their composites, such as their suitability for electronics, environmental applications, thermal management, and energy storage. Challenges and potential opportunities are proposed to offer new insights into prospects of this material.

Simultaneous Solar-Thermal Desalination and Catalytic Degradation of Wastewater Containing Both Salt Ions and Organic Contaminants

Although solar steam generation is promising in generating clean water by desalinating seawater, it is powerless to totally degrade organic contaminants in the seawater. Herein, solar steam generation and catalytic degradation are integrated to generate clean water by simultaneous solar-driven desalination and catalytic degradation of wastewater containing both salt ions and organic contaminants. Stepwise decoration of three-dimensional nickel foam with polypyrrole, reduced graphene oxide (RGO), and cobalt phosphate is realized to obtain polypyrrole/RGO/cobalt phosphate/nickel foam (PGCN) hybrids for solar-driven desalination and catalytic degradation of wastewater containing antibiotics and salt ions. The oxygen-containing groups of the RGO integrated with the porous nickel foam make the porous PGCN hybrid hydrophilic and ensure the upward transport of water to the evaporation surface, and the oxygen vacancies of the cobalt phosphate allow the PGCN to generate abundant highly active singlet oxygen that could still exhibit excellent catalytic degradation performances in the high salinity and highly alkaline environment of seawater. In addition to the high solar light absorbance and satisfactory solar-thermal conversion efficiency of polypyrrole and RGO, the thermally conductive nickel foam skeleton can effectively transfer the heat generated by the solar-thermal energy conversion to the adjacent cobalt phosphate catalyst and nearby wastewater, achieving a solar-thermal-promoted catalytic degradation of organic contaminants. Therefore, a high pure water evaporation rate of 2.08 kg m-2 h-1 under 1 sun irradiation and 100% catalytic degradation of Norfloxacin and dyes are achieved. The PGCN hybrid is highly efficient in purifying seawater containing 10 ppm Norfloxacin and simultaneously achieves a high purification efficiency of 100 kg m-2 h-1.

Omnidirectionally irradiated three-dimensional molybdenum disulfide decorated hydrothermal pinecone evaporator for solar-thermal evaporation and photocatalytic degradation of wastewaters

Although most solar steam generation devices are effective in desalinating seawater and purifying wastewaters with heavy metal ions, they are ineffective in degrading organic pollutants from wastewaters. Herein, we design novel solar-driven water purification devices by decoration of three-dimensional pinecones with MoS₂ nanoflowers via a one-step hydrothermal synthesis for generating clean water. The vertically arrayed channels in the central rachis and the unique helically arranged scales of the hydrothermal pinecone can not only transfer bulk water upward to the evaporation surface, but also absorb more solar light from different incident angles for solar-thermal evaporation and photodegradation of wastewaters under omnidirectional irradiations. The decorated MoS₂ nanoflowers can not only enhance the solar-thermal energy conversion efficiency, but also decompose organic pollutants in the bulk water by their photocatalytic degradation effects. The resultant hydrothermal pinecone with in situ decorated MoS₂ (HPM) evaporator exhibits a high evaporation rate of 1.85 kg m^-2 h^-1 under 1-sun irradiation with a high energy efficiency of 96 %. During the solar-driven water purification processes, the powdery HPM can also photodegrade organic pollutants of methylene blue and rhodamine B with high removal efficiencies of 96 % and 95 %, respectively. For practical demonstration, by floating in the methylene blue solution under 1-sun irradiation, the bulky HPM can generate clean water by simultaneous solar-thermal evaporation and photocatalytic degradation. The integration of solar steam generation and photocatalytic degradation mechanisms makes the HPM evaporator highly promising for practical high-yield purification of wastewaters.

One-pot synthesis of a cellulose-supported CoFe2O4 catalyst for the efficient degradation of sulfamethoxazole

Cellulose-supported cobalt ferrite (CoFe₂O₄/RC) was synthesized via a facile one-pot hydrothermal method and demonstrated to be an efficient catalyst to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). The characterizations of CoFe₂O₄/RC catalysts revealed that an appropriate particle size of the cellulose support could promote the dispersion of CoFe₂O₄ nanoparticles and consequently promote the catalytic activity of the resulting CoFe₂O₄/RC catalysts. The degradation of SMX reached 97.6 % within 20 min at 30 °C with the CoFe₂O₄/RC/PMS system. The mechanism of SMX degradation over CoFe₂O₄/RC-activated PMS was studied via EPR, XPS, and quenching tests. The results suggested that ¹O₂ was the dominant reactive oxygen species and was accompanied by SO₄^-, OH, and O₂^- radicals for SMX degradation. The CoFe₂O₄/RC catalyst exhibited high stability and recyclability and maintained high catalytic activity after five experimental cycles.

Enhanced photodegradation of reactive dyes in textile effluent with CoFe2O4/g-CN heterostructure-mediated peroxymonosulphate activation

Graphitic carbon nitride (g-C₃N₄) was employed as a sacrificial substructure and two-dimensional support to develop magnetic cobalt ferrite-carbon nitride (CoFe₂O₄/g-CN) composite via a one-step solid combustion method. The catalyst activated peroxymonosulphate (PMS), through the interconversion of Co^2 + /3+|_surf. and Fe^2 + /3+|_surf. on its surface for degradation of reactive dyes (RDs). Excellent ferromagnetic nature (44.15 emu g^-1) of the catalyst led to its efficient magnetic separation. With an optimum catalyst and PMS dose of 0.4 g L^-1 and 1.5 g L^-1, 99% RD removal was achieved for textile effluent (pH 9.5-10), under UV irradiation (48 W). In-depth radical scavenging experiments and EPR analysis confirmed the dominance of radical-based degradation process. Plausible degradation and mineralization pathways of RDs were proposed through identification of intermediates by LCMS/MS analysis. In brief, this study elucidates an exclusive strategy towards the use of g-C₃N₄ as fuel for facile synthesis of magnetic CoFe₂O₄/g-CN as a remarkable photocatalyst for activation of PMS towards mineralization of various industrially relevant RDs.

Oxygen vacancies-enriched CoFe2O4 for peroxymonosulfate activation: The reactivity between radical-nonradical coupling way and bisphenol A

Oxygen vacancies (O_V) play a vital role in catalytic activity. Herein, a series of MOF-derived CoFe₂O₄ nanomaterials with O_V tuned by a simple thermal aging strategy are prepared for peroxymonosulfate (PMS) activation. Remarkably, the stability, structural and catalytic properties show dependence on the annealing temperature. The abundant surface O_V and functional groups on CoFe₂O₄ were verified as active sites to boost catalytic activity. Based on the density functional theory (DFT) calculations, (1 1 1), (2 2 2) and (4 2 2) planes exposed at higher temperatures facilitate catalytic performance, ascribed to the intense surface adsorption energy. The quenching and electron paramagnetic resonance (EPR) experiments indicate catalysis degradation is a radical-nonradical coupling process. The reactivity between reactive oxygen species (ROS) and bisphenol A and the radical-nonradical dual degradation pathways are systematically explored by combined DFT and HPLC-MS.

Development of eco-friendly CO2-responsive cellulose nanofibril aerogels as "green" adsorbents for anionic dyes removal

A novel CO₂-responsive cellulose nanofibril aerogel as a "green" adsorbent derived from poly(methacrylic acid-co-2-(dimethylamino) ethyl methacrylate) and carboxylated cellulose nanofibrils was successfully prepared via stepwise cation-induced gelation and freeze drying method. This aerogel exhibited CO₂-triggered adsorption behavior towards anionic dyes with a rapid adsorption rate and a high adsorption capacity, as well as satisfactory mechanical properties. Upon CO₂ stimulation, the charged aerogel can selectively adsorb anionic dyes from aqueous solutions based on an electrostatic interaction. The maximum adsorption capacities of this aerogel towards methyl blue (MB), naphthol green B (NGB), and methyl orange (MO) were 598.8, 621.1 and 892.9 mg g^-1, respectively, accompanied by fast adsorption equilibriums towards MB and NGB within 7 min, and MO within 12 min. Meanwhile, the adsorption isotherms and the kinetics of the CO₂-responsive adsorbents followed the Freundlich isotherm and the pseudo-second-order model, respectively. Furthermore, the resulting CO₂-responsive adsorbent exhibited outstanding recyclability, as its adsorption performance can still be maintained even after twenty cycles. Accordingly, the resultant CO₂-responsive cellulose nanofibril aerogel could be a promising adsorbent material for the removal of anionic dyes in wastewater remediation.

Facile and Scalable Fabrication of Antibacterial CO2-Responsive Cotton for Ultrafast and Controllable Removal of Anionic Dyes

A novel CO₂-responsive cotton as an eco-friendly adsorbent derived from poly(4-acryloyloxybenzophenone-co-2-(dimethylamino) ethyl methacrylate) and cotton was fabricated via a facile and fast dip-coating method. As expected, upon CO₂ stimulation, the protonated cotton presented CO₂-induced "on-off" selective adsorption behaviors toward anionic dyes owing to electrostatic interactions. The adsorption isotherms and kinetics of the CO₂-responsive cotton toward anionic dyes obeyed the Langmuir isotherm and pseudo-second-order kinetics models, respectively. It is noteworthy that the CO₂-responsive cotton exhibited high adsorption capacity and ultrafast adsorption rate toward anionic dyes with the maximum adsorption capacities of 1785.71 mg g^-1 for methyl orange (MO), 1108.65 mg g^-1 for methyl blue (MB), and 1315.79 mg g^-1 for naphthol green B (NGB), following the adsorption equilibrium times of 5 min for MO, 3 min for MB, and 4 min for NGB. Moreover, the CO₂-responsive cotton also exhibited high removal efficiency toward anionic dyes in synthetic dye effluent. Additionally, the CO₂-responsive cotton could be facilely regenerated via heat treatment under mild conditions and presented stable adsorption properties even after 15 cycles. Finally, the as-prepared CO₂-responsive cotton exhibited outstanding antibacterial activity against E. coli and S. aureus. In summary, this novel CO₂-responsive cotton can be viewed as a promising eco-friendly adsorbent material for potential scalable application in dye-contaminated wastewater remediation.

Synergistic multiple active species for catalytic self-cleaning membrane degradation of persistent pollutants by activating peroxymonosulfate

Recently, the development of dual functional catalytic membrane for the synergistic degradation and filtration of persistent pollutants has attracted considerable attention in environmental remediation. Herein, novel CoFe alloy and CoFe₂O₄ nanoparticles encapsulated in N-doped microtube composites (CoFe-NMTs) were firstly fabricated through in-situ pyrolysis of simple-source Prussian blue analogues (PBA). As expected, this unique structure not only inhibited the nanoparticles agglomeration, but also provided a "highway" that accelerated the Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺ redox cycles. Therefore, CoFe-NMT-800 (0.1 g/L, pyrolyzed at 800 °C) achieved over 90% tetracycline (TC, 30 mg/L, 0.1821 min^-1) removal after 30 min at a wide pH (2.55-9.55) by coupling with peroxymonosulfate (PMS, 0.3 g/L), which dramatically outperformed the majority of the reported catalysts (such as Co₃O₄, CoFe alloy, CoFe₂O₄ and N-doped carbon nanotubes, etc.). Additionally, CoFe-NMTs-800 also exhibited excellent catalytic activity in the existence of inorganic anions (Cl^-, HCO₃^- and H₂PO₄^-) and natural organic matters (humic acid (HA)). Subsequently, CoFe-NMTs-800 was immobilized into polyvinylidene fluoride (PVDF) membrane as catalytic self-cleaning membrane via applying phase-inversion technology. It was found that CoFe-NMTs-800/PVDF membrane not only maintained high removal efficiency for TC degradation (over 90%) in TC/HA coexistence system, but also effectively eliminated the adverse effect of membrane fouling. Besides, the fabricated membrane also showed desirable reusability and neglectable metal leaching (0.003 mg/L Fe and 0.015 mg/L) with almost constant flux after five cycles. The quenching experiments and electron paramagnetic resonance (EPR) results clearly indicated that sulfate radicals (SO₄^-), hydroxyl radicals (OH and singlet oxygen (¹O₂) were responsible for TC degradation and SO₄^- was a major contributor. Significantly, this work was very meaningful to construct novel catalytic self-cleaning membrane for water purification.

Super-fast degradation of high concentration methyl orange over bifunctional catalyst Fe/Fe3C@C with microwave irradiation

Bifunctional catalyst Fe/Fe₃C@C with magnetism was successfully prepared by sol-gel method and proved to degrade methyl orange with high efficiency under microwave irradiation. The Fe/Fe₃C@C catalysts calcined at 500 °C, 600 °C, 700 °C were intensively characterized and compared in their crystalline structure, porosity, morphology and dielectric property. The results imply a phase and structure transformation in the materials as the calcination temperature increased. Fe/Fe₃C@C-700 exhibited a core-shell structure and an apparent Fe₃C phase. In addition, Fe/Fe₃C@C-700 demonstrated excellent dielectric property as a microwave absorber than Fe/Fe₃C@C-500 and Fe/Fe₃C@C-600. At the same time, it gave a 100 % removal rate in 30 s for the degradation of methyl orange under microwave irradiation, outperformed the Fe/Fe₃C@C-500 and Fe/Fe₃C@C-600 and most other reported catalysts in similar studies. The possible mechanism of the methyl orange degradation should be ascribed to the in situ generation of ^•OH and O₂^•- active species over the Fe/Fe₃C@C catalyst. The excellent microwave absorbing property of Fe/Fe₃C@C-700 could also boost its catalytic activity and play a critical role during the super-fast microwave-assisted degradation process. The findings in this study could be informative for the development of a continuous process of dye wastewater treatment for industrial implementation.

Controlled Synthesis of Manganese Oxide Nanoparticles Encaged in Hollow Mesoporous Silica Nanoreactors and Their Enhanced Dye Degradation Activity

In this study, controlled synthesis of hollow mesoporous silica nanoreactors with small manganese oxide nanoparticles in their cavities (Mn _x O _y @HMSNs) is reported, and the dye degradation performance in the presence of hydrogen peroxide over Mn _x O _y @HMSNs is investigated. Specifically, triple ligands (a compound with three dipicolinic acid groups) were used to coordinate manganese ions to form negatively charged coordination complex networks, which further combine with positively charged copolymers to obtain metal ion-containing polymer micelles. Following silica deposition onto micellar coronas and calcinations simultaneously result in hollow mesoporous silica nanoreactors and manganese oxide nanoparticles in their cavities. In this work, the influences of synthetic parameters on the structures are studied in detail. The obtained Mn _x O _y @HMSNs show greatly enhanced activity and stability for a series of dye degradations. The performance enhancement is ascribed to their unique nanostructures, where mesoporous silica walls provide protection to the inner Mn _x O _y nanoparticles and the small size of the manganese oxide nanoparticles greatly enhances the dye degradation activity.

Heterogeneous activation of persulfate by ZnCoxFe2−xO4 loaded on rice hull carbon for degrading bisphenol A

Mechanism of the activation on PS by ZnCo_1.3Fe_0.7O₄-RHC for the degradation of BPA.