Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo₂O₄ <i>In Situ</i> Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation–hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g–1 (1503.3 C g–1) at 1 A g–1, a superior rate performance of 2335.2 F g–1 at 20 A g–1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg–1 at a power density of 800 W kg–1, and the energy density at a peak power density of 20004 W kg–1 still remained at 48.9 Wh kg–1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4‑Nitrophenol Reduction

A series of Co-doped ternary CuxCo3–xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The CuxCo3–xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The CuxCo3–xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu1.5Co1.5Al-LDH/rGO with the highest kapp value of 49.2 × 10–3 s–1 and TOF of 232.8 h–1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH#, ΔS#, and ΔG# were estimated. The best activity of Cu1.5Co1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu2O NPs (∼4.3 nm) along with a small amount of Cu0 species, the electron transfer effect induced by atomically dispersed Co2+ species leading to the formation of electron-rich Cu species along with the Co2+/Co3+ redox couple, the strong Cu2O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π–π stacking via an rGO layer. Meanwhile, the Cu1.5Co1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu1.5Co1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4‑Nitrophenol Reduction

A series of Co-doped ternary CuxCo3–xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The CuxCo3–xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The CuxCo3–xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu1.5Co1.5Al-LDH/rGO with the highest kapp value of 49.2 × 10–3 s–1 and TOF of 232.8 h–1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH#, ΔS#, and ΔG# were estimated. The best activity of Cu1.5Co1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu2O NPs (∼4.3 nm) along with a small amount of Cu0 species, the electron transfer effect induced by atomically dispersed Co2+ species leading to the formation of electron-rich Cu species along with the Co2+/Co3+ redox couple, the strong Cu2O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π–π stacking via an rGO layer. Meanwhile, the Cu1.5Co1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu1.5Co1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater

Magnetically Double-Shelled Layered Double Oxide (LDO)/LDO/γ-Fe₂O₃ Composite for Highly Efficient Removal of Congo Red and Chromium(VI)

Novel double-shelled core-shell-type magnetic composites MgFexAl-LDO/LDO/γ-Fe2O3 (x = 0, 0.1, and 0.5) were synthesized by a cost-effective two-step coprecipitation method followed by proper calcination. The composites are constructed by two layers of LDO nanosheets (∼80 × 10 nm) which shows vertically oriented relay growth on the surface of spherical γ-Fe2O3. The thickness of LDO shells is ca. 220 ∼ 260 nm, providing a large number of effective adsorption sites and numerous open channels composed of adjacent LDO nanosheets. All the composites show excellent adsorption capacities for Congo Red (CR) and Cr­(VI). Especially, the MgAl-LDO/LDO/γ-Fe2O3 exhibits the maximum adsorption capacity (qmax = 123.4 mg g–1) for Cr­(VI), which is due to the double-shelled morphology with a large Brunauer–Emmett–Teller area (219 m2 g–1), the electrostatic attraction between the positive LDO shells and Cr­(VI) oxyanions, and the adsorption-coupled reduction, with the adsorbed Cr­(VI) anion reduced to Cr­(III) by hydroxyl groups of the hydrated metal ions and reconstructed into layer double hydroxide layers by the “memory effect”. The MgAl-LDO/LDO/γ-Fe2O3 and MgFe0.1Al-LDO/LDO/γ-Fe2O3 show extraordinary adsorption efficiency for CR with very close qmax values (3980 and 3832 mg g–1, respectively). The former can be attributed to its large SBET and strong LDO shellsCR anion electrostatic interaction, while the latter (99 m2 g–1) can still be ascribed to the complexing function of a small amount of Fe3+ species to CR. The MgAl-LDO/LDO/γ-Fe2O3 composite can be conveniently separated and recovered from the aqueous solution after adsorption by an external magnet. The fourth cycle efficiency of up to 84% implies a promising application prospect

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4‑Nitrophenol Reduction

A series of Co-doped ternary CuxCo3–xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The CuxCo3–xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The CuxCo3–xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu1.5Co1.5Al-LDH/rGO with the highest kapp value of 49.2 × 10–3 s–1 and TOF of 232.8 h–1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH#, ΔS#, and ΔG# were estimated. The best activity of Cu1.5Co1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu2O NPs (∼4.3 nm) along with a small amount of Cu0 species, the electron transfer effect induced by atomically dispersed Co2+ species leading to the formation of electron-rich Cu species along with the Co2+/Co3+ redox couple, the strong Cu2O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π–π stacking via an rGO layer. Meanwhile, the Cu1.5Co1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu1.5Co1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4‑Nitrophenol Reduction

A series of Co-doped ternary CuxCo3–xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The CuxCo3–xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The CuxCo3–xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu1.5Co1.5Al-LDH/rGO with the highest kapp value of 49.2 × 10–3 s–1 and TOF of 232.8 h–1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH#, ΔS#, and ΔG# were estimated. The best activity of Cu1.5Co1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu2O NPs (∼4.3 nm) along with a small amount of Cu0 species, the electron transfer effect induced by atomically dispersed Co2+ species leading to the formation of electron-rich Cu species along with the Co2+/Co3+ redox couple, the strong Cu2O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π–π stacking via an rGO layer. Meanwhile, the Cu1.5Co1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu1.5Co1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater

Highly Dispersed Pd Nanoclusters on Layered Double Hydroxides with Proper Calcination Improving Solvent-Free Oxidation of Benzyl Alcohol

Highly dispersed Pd nanocluster (NC) catalysts x-PdNCs/LDH-T (where x is the Pd loading, T is the calcination temperature, and LDH refers to Ni3Al-layered double hydroxides) were synthesized by the electrostatic adsorption of atomically precise captopril (Capt)-protected Pd17Capt8 clusters (∼1.4 nm) onto the LDH support followed by proper calcination. The 0.15-PdNCs/LDH-T (where T = 250, 270, and 280 °C) catalysts show similar Pd NCs with sizes of ∼1.6 nm highly distributed on the verge of small-sized LDH nanoplates (30–50 × ∼15 nm), while the 0.16-PdNCs/LDH-300 catalyst shows slightly increased Pd NCs size of ∼1.8 nm, attributable to the sintering between neighboring NCs. The as-obtained catalysts x-PdNCs/LDH-T all show excellent solvent-free aerobic oxidation activity of benzyl alcohol, and 0.15-PdNCs/LDH-280 exhibits the highest turnover frequency of 108,670 h–1. This unprecedented activity can be attributed to the ultrafine Pd NCs with the complete exposure of interfacial sites Pd0/Pd2+–Ni2+–OH after removing the surface ligands contributing to the adsorption and activation of the reactants, the electron-rich Pd0 species stemmed from the electron transfer from Ni2+–OH groups to Pd clusters promoting the β-hydride elimination of metal-alkoxide intermediates and strong PdNCs–LDH synergistic interactions, while other catalysts with residual ligands or enlarged PdNCs along with less surface hydroxyls as well as a newly generated NiO phase exhibit reduced activity owing to the blocked or reduced active sites. Additionally, the present catalyst shows no significant activity loss after six runs, indicating its excellent recyclability

Hierarchical-Structured Pd Nanoclusters Catalysts <i>x</i>‑PdNCs/CoAl(O)/rGO‑<i>T</i> by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4‑Nitrophenol Reduction

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd17Capt8 NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co3Al-layered double hydroxide/reduced graphene oxide (Co3Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl­(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl­(O) nanosheets. All of the x-PdNCs/CoAl­(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl­(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h–1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl­(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs–Co2+-OH­(LDH)–rGO three-phase synergy, and the much improved adsorption of the substrate via π–π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl­(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants

Hierarchical-Structured Pd Nanoclusters Catalysts <i>x</i>‑PdNCs/CoAl(O)/rGO‑<i>T</i> by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4‑Nitrophenol Reduction

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd17Capt8 NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co3Al-layered double hydroxide/reduced graphene oxide (Co3Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl­(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl­(O) nanosheets. All of the x-PdNCs/CoAl­(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl­(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h–1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl­(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs–Co2+-OH­(LDH)–rGO three-phase synergy, and the much improved adsorption of the substrate via π–π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl­(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants

Hierarchical-Structured Pd Nanoclusters Catalysts <i>x</i>‑PdNCs/CoAl(O)/rGO‑<i>T</i> by the Captopril-Capped Pd Cluster Precursor Method for the Highly Efficient 4‑Nitrophenol Reduction

Water-soluble captopril-capped atomically precise Pd nanoclusters (Pd17Capt8 NCs: 1.3 ± 0.5 nm) produced by a simple chemical reduction were supported on preprepared hybrid Co3Al-layered double hydroxide/reduced graphene oxide (Co3Al-LDH/rGO) by a pH-adjusted electrostatic adsorption strategy followed by proper calcinations, giving a series of novel catalysts x-PdNCs/CoAl­(O)/rGO-T (x (Pd loading) = 0.09, 0.17, 0.43 wt % (ICP), T = 230, 250, 280, 300, 320 °C). The characterization results show that the as-obtained catalysts possess the hierarchical nanosheet array morphology. Pd NCs with a size of ∼1.3 to 1.8 nm are highly distributed at the edge sites of the CoAl­(O) nanosheets. All of the x-PdNCs/CoAl­(O)/rGO-T catalysts show superior catalytic efficiency for the conversion of 4-nitrophenol to 4-aminophenol, particularly 0.17-PdNCs/CoAl­(O)/rGO-300 possesses the highest performance with a turnover frequency (TOF) of 30 042 h–1, which is the highest among the reported Pd-based catalysts so far. The superior activity of 0.17-PdNCs/CoAl­(O)/rGO-300 can be owing to ultrafine Pd NCs with a clean surface, the strongest PdNCs–Co2+-OH­(LDH)–rGO three-phase synergy, and the much improved adsorption of the substrate via π–π stacking upon nanosheet array morphology. Meanwhile, 0.17-PdNCs/CoAl­(O)/rGO-300 exhibits excellent catalytic activities for various nitroarenes and anionic azo dyes as well as good reusability with the complete reduction of 4-nitrophenol (4-NP) within 90 s after 10 successive runs. The present work provides not only a simple and convenient strategy for the synthesis of clean, efficient, and environmentally friendly supported metal nanocluster catalysts but also a new idea for the efficient catalytic degradation of environmental pollutants