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Phenylurea herbicide residuals in soil may continuously contaminate surface water and groundwater due to unregulated and improper use. Herein, we reported a stable and active oxidation system including heterogeneous Fe-based layered double hydroxide materials as persulfate (PS) activators. Under mild conditions, 1% LDH in weight and 70 mM PS can completely degrade 500 mg/kg isoproturon in soil within 10 h, during which less than 0.1 ppm heavy metal leaching was detected. This remarkable performance was consistent in a broad pH range (3~11) and was resistant to various inorganic anions (Cl - , Br - , NO 3 - , HCO 3 - ) and humic acid. Mechanism studies from scavenging tests, EPR, and fluorescence spectra collectively proved that besides •OH and •SO 4 - , singlet oxygen ( 1 O 2 ) and superoxide (•O 2 - ) were also generated and were accounted for the oxidative degradation. This unique mechanism of generating diverse radicals was clearly distinguished from classic Fe(II)/PS system, significantly reduced the influence of varying parameters in water and soil matrix, and was suggestive to chemical oxidation system in soil remediation to avoid scavenging effects by background electrolytes or other components in water/soil matrix. Graphical abstract ᅟ.

The agglomeration of rGO resulted from the morphological irregularities restrict its direct applications as catalyst for pollutants removal using advance oxidation processes (AOPs). In this study, we addressed this problem after incorporating the nanosheets of reduced graphene oxide (rGO) in the layers of hydroxides (LDHs) as Fe-rGO LDH hetero-composite. Based on the first order kinetic model, the fabricated composite showed excellent phenol removal with degradation rate constant of 0.16 min−1, 5–100 times higher than Fe-LDH/rGO or other control catalysts. This enhanced catalytic activity was resulted from the systematic assembly of both monolayered rGO and LDHs as superlattice materials, avoiding the aggregation of rGO during the reaction and thus promote the interfacial electron transfer among the active sites. Moreover, Fe-rGO LDH/PMS system exhibited consistent performance over a wide pH range (3.0 ─ 12.0) and broad spectrum of co-existing water constituents (anions and humic acid). The spectroscopic and analytical results suggested that the special arrangement of monolayered rGO in Fe-LDHs facilitated Fe sites to form a stable Fe intermediates after reacting PMS, offering a suitable centre to accept electron from another PMS to generate superoxides (•O 2 −). Finally, singlet oxygen (1O 2) was accounted as dominant reactive oxygen species (ROS) for pollutants removal. Image 1 [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe-HO/(NO 3) captured GO excellently than hydroxides with different anions. • NO 3 – release from the hydroxide galleries resulted in exfoliation of host layers. • Electrostatic interactions were the driving force for removal of GO. • GO removal was significantly affected by pH. • Coagulated end product was further used in secondary applications, i.e., AOPs and adsorption. The extensive use and inevitable release of graphene oxide (GO) to the environment have increased the threat of its exposure to living organisms. This study reports the design of Fe-based hydroxides with different interlayers anions, i.e., Cl−, SO 4 2−, CO 3 2−, and NO 3 − to capture GO from an aqueous medium. Various characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared (FTIR), and scanning electron microscopy (SEM), confirmed the successful synthesis of these different materials. The Fe-hydroxides as Fe-HO/(NO 3) with NO 3 − interlayers anions effectively removed up to 190 mg/g GO and was tolerant to a high concentration of background electrolyte, different anions, and increasing ionic strength. These remarkable features of Fe-HO/(NO 3) originated from the weak bonding abilities of interlayers NO 3 − anions that facilitated simple self-exfoliation of hydroxide nanosheets, and thus promoted the electrostatic interactions between the positively charged layers of hydroxides and negatively charged GO particles. The coagulated end product (Fe-HO/(NO 3)@GO can be further used in advanced oxidation processes (AOPs) as catalyst or adsorbent for the treatment of different pollutants. We believe that this work not only explains the positive aspect of regulating anions in the hydroxides layers but also provides a direction to develop new materials for environmental remediation. [ABSTRACT FROM AUTHOR]

• Cu-rGO LDH nanohybrid fabricated by intercalating rGO inside the LDH galleries. • Cu-rGO LDH exhibited higher surface area and electrical conductivity. • Cu-rGO LDH/PMS induced nonradical pathway. • 1O 2 generated through SO 5 − owing to electron conduction between PMS and Cu2+. A new strategy was applied by periodic stacking of active sites of Cu and reduced graphene oxide (rGO) in the form of Cu-rGO LDH nanohybrid material. The experimental results revealed that newly prepared Cu-rGO LDH nanohybrid material was extremely reactive in PMS activation as evident from the degradation rate of 0.115 min−1, much higher than Mn-rGO LDH (0.071 min−1), Zn-rGO LDH (0.023 min−1) or other benchmarked material used during the degradation of bisphenol A (BPA). This excellent activity of Cu-rGO LDH nanohybrid was attributed to the better PMS utilization efficiency as compared to the other catalysts. Additionally, the characterization techniques disclosed that the layer by layer arrangement of active sites in the Cu-rGO LDH catalyst promotes interfacial electron mobility owing to the synergistic association between Cu in LDH and interlayered rGO. Based on the in-situ electron paramagnetic resonance spectroscopy (EPR) and chemical scavengers, singlet oxygen (1O 2) was unveiled as dominant reactive species for pollutant removal, resulting from the recombination of superoxides (O 2 −) or reduction of active Cu centers. We believe that this novel Cu-rGO LDH/PMS system will open up a new avenue to design efficient metal-carbon nanohybrid catalysts for the degradation of emerging aquatic pollutants in a real application. [ABSTRACT FROM AUTHOR]

• Synergistic effect of Cu and Co oxides was find on various supports. • Incorporation of Cu changed the activation pathway of PMS by Co catalysts. • Surface hydroxyl groups on catalysis was studied quantitatively. • Electron transfer between Cu and Co improved the stoichiometric efficiency of PMS. Synergistic effect was commonly observed in bimetallic oxide catalysts in sulfate radical-based advanced oxidation processes by forming spinel structures. In this paper, we found the incorporation of Cu demonstrated the most remarkable promotional effect to Co oxides comparing with Fe and Mn in PMS activation, and no spinel structure of mixed metals was found. Moreover, the synergism between oxides of Cu and Co was observed on various supports including MgAl layered double hydroxides, mesoporous MnO 2 and ZnO. Under conditions of 0.2 g L−1 catalysts, 2 mM PMS, and 40 ppm 4-chlorophenol (4-CP), CuCo@ZnO/PMS system demonstrated excellent performance that 96.0% 4-CP could be removed, while the removal efficiency of 4-CP in Cu@ZnO/PMS and Co@ZnO/PMS systems was only 12.1% and 45.4%, respectively. The simultaneous incorporation of Co and Cu bimetallic oxides in CuCo@ZnO led to a higher surface hydroxyl density, and this surface hydroxyl density showed a linear relationship to their first order kinetic constant in 4-CP degradation. Moreover, the results of peroxymonosulfate (PMS) decomposition, quantification of sulfate radical (SO 4 −), EPR, XPS, H 2 -TPR, and CV indicated that the synergism of Cu/Co also arose from the electron transfer between Cu(I) and Co(III), which altered the redox circle of Co(II)/Co(III) and increased the steady concentration of oxidative radicals. Due to this synergism, the degradation percentage of organic contaminants, stability of heterogeneous catalysts and the stoichiometric efficiency of PMS were all improved. These findings were highly suggestive to the further development of bimetallic heterogeneous catalysts in persulfate based advanced oxidation processes. [ABSTRACT FROM AUTHOR]