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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]

Abstract The designing of selective and efficient adsorbent for removal of heavy metals from wastewater of diverse chemistry is a challenging task for researchers. Herein, FeMgAl derived from layered double hydroxides (LDH) with different intercalated anions (CO 3 2−, NO3−, S 5 2− and MoS 4 2−) as selective adsorbents were evaluated by considering capturing heavy metals from a complex aqueous environment such as: 1) adsorption of single metals ions from a mixture of Ag+, Hg2+, Pb2+, Cu2+, Cd2+, Co2+, Ni2+, Zn2+, 2) adsorption of heavy metals in the presence of huge amount of Ca2+, Mg+, Na+, Cl−, NO 3 − and SO 4 2− ions, 3) adsorption under different solution pHs, 4) solutions with high salinity etc. Out of the studied materials, fast kinetics, record capacities (582 for Hg2+ and 565 mg/g for Ag+) with enormous K d values (1.0 × 108–2.5 × 107) placed FeMgAl MoS 4 (Fe MoS 4 LDH) as the most selective and promising material. FeMgAl S 5 (Fe S 5 LDH) was also impressive due to its good capacities (279 mg/g for Hg2+ and 341 mg/g for Ag+ ions) with K d values (8.3 × 105–1.0 × 103). In contrast, FeMgAl CO 3 and FeMgAl NO 3 (Fe CO 3 LDH and Fe NO 3 LDH) showed very poor selectivity, lower capacities and very small K d values. Furthermore, Fe MoS 4 LDH and Fe S 5 demonstrated negligible efficiency loss in the presence of competitive cations/anions or with change in solution pH. As confirmed by X-ray Diffraction (XRD) and Fourier Transformed Infrared (FTIR) analysis, a mechanism for adsorbed metals in the form of various coordinated complexes inside LDH layers was proposed for Fe MoS 4 or Fe S 5 LDHs. In contrast, a dominant precipitation mechanism as metal-hydroxide or metal-carbonate was suggested for Fe CO 3 and Fe NO 3 LDHs. Graphical abstract Image 1 Highlights • Adsorption by Fe-LDHs with different intercalated anions was compared. • Intercalating with sulfides functional groups offered excellent selectivity. • Adsorption performance was consistent in diverse types of wastewater. • Distinguished adsorption mechanism was proposed. [ABSTRACT FROM AUTHOR]

The designing of efficient, selective and stable adsorbents for heavy metals removal remained a challenging task, as most adsorbents did not exhibit consistent performance in diverse types of water. Unlike traditional adsorbents based on surface oxygen groups, thio-functionalized layered double hydroxide (LDH) as Mn-MoS 4 was designed by inserting MoS 4 2− anions into lamellar layers in LDH, and was applied as a highly stable, efficient and selective adsorbent for heavy metals removal. The record high distribution coefficient (K d ∼ 10 7 –10 8 mL/g), fast kinetics and enormous saturated uptake capacities (594, 564 & 357 mg/g) for Hg 2+ , Ag + and Pb 2+ placed Mn-MoS 4 as the most efficient adsorbent for the removal of such metals so far. Further, Mn-MoS 4 can completely tolerate the impact of huge concentration of background electrolytes (Ca 2+ , Mg 2+ , Na + , Cl − , NO 3 − & SO 4 2− ), and effectively control the concentrations of Hg 2+ , Ag + and Pb 2+ ions from tap water, lake water or industrial wastewater far below the limitation in drinking water. Similarly, Mn-MoS 4 is a potential filter due to its consistent performance over a broad pH range (from 2.0 to 11.0), changing ionic strength (up to 100 mM) or in the presence of organic matters. These remarkable features originate from the dominant chemical adsorption mechanism through inner-sphere coordination between thio groups as soft Lewis acid and Hg 2+ , Ag + and Pb 2+ as soft Lewis bases. More interestingly, LDH layers offer protective space for intercalated MoS 4 2− anions against oxidation, and facilitate Mn-MoS 4 with the advantage of easy storage and application over other adsorbents. [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]