Enhanced polarization of electron-poor/rich micro-centers over nZVCu-Cu(II)-rGO for pollutant removal with H2O2.

Nanoscale zero-valent copper combined with Cu(II)-doped reduced graphene oxide hybrid (nZVC-Cu(II)-rGO) is synthesized through an annealing reduction process, and it shows very high activity and efficiency for removing refractory organic compounds with H2O2. The conversion rate for the organic pollutant in this system is ∼77 and ∼13 times higher than that in the graphene oxide (GO) and reduced graphene oxide (rGO) systems, respectively. The characterization shows that nanoscale Cu(0) and Cu(II) are generated on the rGO surface during the annealing process and they are accompanied by the COCu bonding formation between the rGO substrate and the Cu(II) species in nZVC-Cu(II)-rGO, which induces cation-π interactions on the surface, resulting in the reinforced electron-rich micro-centers formation around the nZVC-enhanced Cu(II) species and electron-poor micro-centers on rGO-aromatic rings. The generation of nanoscale Cu(0) consolidates the polarization of the dual reaction micro-centers and greatly accelerates the electron transfer of the system, thus promoting H2O2 reduction to OH in the electron-rich micro-centers. Pollutants can obviously replace H2O2 as the electron donors of the system and are efficiently oxidized and degraded in the electron-poor micro-centers, with their own electron energy being fully utilized in the nZVC-Cu(II)-rGO Fenton-like system.

Notable light-free catalytic activity for pollutant destruction over flower-like BiOI microspheres by a dual-reaction-center Fenton-like process.

BiOI is widely used as photocatalysts for pollutant removal, water splitting, CO2 reduction and organic transformation due to its excellent photoelectric properties. Here, we report for the first time that a light-free catalyst consisting of the flower-like BiOI microspheres (f-BiOI MSs) exposing (1 0 1) and (1 1 0) crystal planes prepared by a hydrothermal method in ethylene glycol environment can rapidly eliminate the refractory BPA within only ∼3 min through a Fenton-like process. The reaction activity is ∼190 times higher than that of the conventional Fenton catalyst Fe2O3. A series of characterizations and experiments reveal the formation of the dual reaction centers on f-BiOI MSs. The electron-rich O centers efficiently reduce H2O2 to OH, while the electron-poor oxygen vacancies capture electrons from the adsorbed pollutants and divert them to the electron-rich area during the Fenton-like reactions. By these processes, pollutants are degraded and mineralized quickly in a wide pH range. Our findings address the problems of the classical Fenton reaction and are useful for the development of efficient Fenton-like catalysts through constructing dual reaction centers.

Efficient Destruction of Pollutants in Water by a Dual-Reaction-Center Fenton-like Process over Carbon Nitride Compounds-Complexed Cu(II)-CuAlO2.

Carbon nitride compounds (CN) complexed with the in-situ-produced Cu(II) on the surface of CuAlO2 substrate (CN-Cu(II)-CuAlO2) is prepared via a surface growth process for the first time and exhibits exceptionally high activity and efficiency for the degradation of the refractory pollutants in water through a Fenton-like process in a wide pH range. The reaction rate for bisphenol A removal is ∼25 times higher than that of the CuAlO2. According to the characterization, Cu(II) generation on the surface of CuAlO2 during the surface growth process results in the marked decrease of the surface oxygen vacancies and the formation of the C-O-Cu bridges between CN and Cu(II)-CuAlO2 in the catalyst. The electron paramagnetic resonance (EPR) analysis and density functional theory (DFT) calculations demonstrate that the dual reaction centers are produced around the Cu and C sites due to the cation-π interactions through the C-O-Cu bridges in CN-Cu(II)-CuAlO2. During the Fenton-like reactions, the electron-rich center around Cu is responsible for the efficient reduction of H2O2 to •OH, and the electron-poor center around C captures electrons from H2O2 or pollutants and diverts them to the electron-rich area via the C-O-Cu bridge. Thus, the catalyst exhibits excellent catalytic performance for the refractory pollutant degradation. This study can deepen our understanding on the enhanced Fenton reactivity for water purification through functionalizing with organic solid-phase ligands on the catalyst surface.

Theoretical and experimental evidence for rGO-4-PP Nc as a metal-free Fenton-like catalyst by tuning the electron distribution.

The application of the classical Fenton reaction has long been limited by several problems, such as metallic sludge and narrow pH range, which derived from the metal components in the catalyst. Developing a metal-free Fenton catalyst may efficiently address these problems. Here, we firstly perform a density functional theory (DFT) study to explore the possibility of developing the 4-phenoxyphenol molecule-doped reduced graphene oxide nanocomposite (rGO-4-PP Nc) as a metal-free Fenton-like catalyst by tuning the electron distribution. The theoretical calculation results reveal that rGO-4-PP Nc can act as an efficient Fenton-like catalyst for H2O2 activation and pollutant degradation through formation of electron-rich O and electron-deficient C centers on the C-O-C bridge. The actual rGO-4-PP Nc is also prepared via a surface complexation and copolymerization process. The experimental evidence, such as that gained from XRD, FIIR and EPR analysis, confirm the theoretical models and the dual-reaction-center Fenton-like mechanism. This work provides a basis for theoretical calculation to guide the actual synthesis and prediction of catalytic activity of the Fenton-like catalysts, and also offers a creative perspective to develop new generation metal-free Fenton catalysts by tuning the electron distribution using organic polymers.