•AuNPs-modified diamond-based nanocomposite catalysts.•Provide excellent catalytic performance of 4-nitrophenol.•The composite catalyst demonstrates good stability and reusability.The diamond-based hierarchical AuNPs-modified nanocomposites materials were prepared via the synthesis of diamond@graphite building block and polyallylamine hydrochloride (PAH)/polyacrylic acid (PAA) layer-by-layer (LbL) assembled strategy. And the modified gold nanoparticles were carried out by the reduction of aqueous HAuCl4 solution using the reductant NaBH4. The obtained layer-by-layer nanocomposites demonstrate obvious advantages such as high specific surface area, pore diameter and pore volume, providing a higher chance of gold nanoparticles accessible to the reactants. Thus the core–shell nanostructures from of LbL-assembled and diamond-based composite materials are beneficial to improve the catalytic capacity of gold nanoparticles and separation rate from the reactants. In order to testify the enhancement of hierarchical diamond-based AuNPs-modified nanocomposites catalytic activity and utility, the catalytic experiments of 4-nitrophenol solution were well accomplished. The prepared nanocomposites exhibited high activity and demonstrated high recyclability without less weight of gold nanoparticles after eight runs of catalysis reduction of 4-nitrophenolm showing potential application in composite catalytic materials.Download high-res image (164KB)Download full-size image

•Silver decorated LaMnO3 nanorod/reduced graphene oxide composite were synthesized for the first time.•Composite has the high decolourization ratio for direct green BE.•Composite has the excellent recycle stability of photo catalytic.A new nanostructure photocatalyst, incorporating Ag and reduced graphene oxide (rGO) with LaMnO3-nanorods have been fabricated via two-step synthetic approaches by using Cetyltrimethyl Ammonium Bromide (CTAB) as a template via a simple hydrothermal reaction and the decoration of Ag nanoparticles is through a traditional silver mirror reaction. The characteristic of the materials are examined by XRD, TEM, FE-SEM and XPS. The results confirm that the LaMnO3 nanorods are perovskite phase and uniform dispersed on the surface of rGO. The Ag nanoparticles is deposited the surface of LaMnO3-nanorods with its metal form. The Ag/LaMnO3-nanorods/rGO exhibit an excellent performance in the photo-degradation of Direct Green BE under the UV-vis irradiation. As an electron capture agent, metal Ag can capture the e− that transported along the LMO-NR, thereby leading to effective separation of the e−-h+ pairs and accelerate the transfer of surface charge, which is further demonstrated by the Photoluminescence (PL) spectra, cyclic voltammetry (CV) and AC impedance spectra.Ag-modified LaMnO3 nanorod/reduced graphene oxide composite possess excellent photocatalytic activity due to the acceleration of surface charge transfer induced by the dispersive Ag.

•LaMn1-xCoxO3–graphene composites were synthesized for the first time.•Oxygen reduction reaction activity of composites in alkaline medium was evaluated.•The electrocatalytic activity of composites was enhanced than pure LaMnO3 oxides.Cobalt doped LaMnO3-graphene composites are prepared by sol-gel process assisted with chelating effect of citric acid. The structure, morphology and valence state of samples are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS). Results show that LaMn1-xCoxO3 particles are homogeneously dispersed on graphene nanosheets, and that doping Co does not change the pervoskite structure. Electrochemical properties are characterized by rotating disk electrode (RDE), rotating ring-disk electrode (RRDE), galvanostatic discharge and AC impedance spectra techniques. The sample prepared with x = 0.1 possesses excellent electrocatalytic activity for oxygen reduction reaction (ORR) and good electrochemical stability in alkaline medium. The measurements of RDE and RRDE reveal that the electron transfer number of LaMn0.9Co0.1O3-graphene is calculated to be 3.87. All the above results indicate that the LaMn1-xCoxO3-graphene composites are promising catalysts with a high catalytic activity toward ORR.Cobalt doped porous LaMnO3-graphene composites possess excellent electrocatalytic activity for oxygen reduction reaction and good electrochemical stability in alkaline medium.

Silver-modified LaMnO3–reduced graphene oxide (RGO) composites are synthesized via a sol–gel method with citric acid as a chelating agent. The as-prepared nanocomposites are characterized via X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The XRD results show that decorating with Ag does not change the perovskite structure and it is metal form. The electrocatalytic activities of the composites for the oxygen reduction reaction are evaluated. The 2 wt% Ag/LaMnO3–RGO as the air cathode catalyst shows a high voltage plateau. The corresponding oxygen reduction reaction mainly favors a four-electron transfer process, exhibits a maximum cathodic current density of 5.45 mA cm−2 at 1600 rpm, and displays good stability (i/i0 = 92.9% at −0.3 V after 30000 s with a rotation rate of 1600 rpm), which is better than that of the commercial Pt/C (20 wt% Pt on carbon) electrocatalyst at the same testing conditions. Such excellent catalytic activity is attributed to the synergistic effect of Ag, LaMnO3, and graphene in the composite, which provide numerous reactive sites and the modification of Ag shortens the conduction path of adsorbed oxygen, thus reducing charge transfer resistance and improving cathode performance.

Ag-modified LaMnO3–graphene nanocomposites were successfully synthesized by the sol–gel technique. The nanocomposites were characterized by X-ray diffraction, field-emission scanning electron microscopy with energy dispersive spectrometer, transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area analysis and photoluminescence analysis. High-efficiency degradation of Direct Green BE under UV-vis light was achieved for Ag/LaMnO3–graphene as photocatalyst. The enhancement of UV-vis photocatalytic activity can be attributed to the high separation efficiency of photoinduced electron–hole pairs resulting from the excellent conductivity of Ag in composites and the formation of multistage drill way, which can promote the adsorption of organic dyes and improve the transfer efficiency of the photocatalytic process. The photocatalytic mechanism was studied by adding hydroxyl radical (˙OH), superoxide radical (˙O2−), and active hole (h+) scavengers. The results confirmed that h+ generated in Ag/LaMnO3–graphene played a key role in photocatalysis, with the assistance of ˙OH. By contrast, ˙O2− had the least influence on the process.

•La1-xCaxMnO3–graphene composites were synthesized for the first time.•Oxygen reduction reaction activity of composites in alkaline medium was evaluated.•The electrocatalytic activity of composites was enhanced than pure LaMnO3 oxides.•Doping Ca enhance the electrochemical performance of LaMnO3–graphene composites.La1−xCaxMnO3 perovskite–graphene composites are synthesized as catalysts for Zn-air cell cathodes. The samples are characterized by thermogravimetry-differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Results show that perovskite particles are homogeneously dispersed on graphene nanosheets, and that doping Ca does not change the perovskite structure. Electrochemical properties are investigated by galvanostatic discharge, linear sweep voltammetry, and electrochemical impedance spectroscopy techniques. LaMnO3–graphene composites show superior performance than pure LaMnO3. Doping Ca into the composites can tune their catalytic activity and sample prepared with x = 0.4 possesses the highest electrocatalytic activity. The measurement of the rotating ring-disk electrode reveals that the electron transfer number of La0.6Ca0.4MnO3–graphene is 3.6. These results indicate that the La1−xCaxMnO3–graphene composites are potential air electrodes catalysts.

•LaMnO3–graphene nanocomposite photocatalysts were synthesized by a sol–gel method for the first time.•The photocatalytic activity was higher than the pristine LaMnO3 after they were hybridized by graphene.•The mechanism for the enhanced photocatalytic performance of LaMnO3–graphene was discussed.LaMnO3–graphene nanocomposite photocatalysts were synthesized by a sol–gel method for the first time. The as-prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller surface area analysis, Raman spectroscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse spectroscopy. Pure LaMnO3 perovskite phase was successfully processed. It anchored on the surface of graphene sheets and had good dispersion behavior. This observation confirmed that the proposed technique was effective. High-efficiency degradation of acid red A under UV–vis light was achieved for the photocatalysts. The photocatalytic efficiency of the LaMnO3–graphene nanocomposites was higher than that of pristine LaMnO3. The enhancement of UV–vis photo catalytic light activity can be attributed to the high separation efficiency of photoinduced electron−hole pairs resulting from the excellent conductivity of graphene in LaMnO3–graphene and the large surface contact between graphene and LaMnO3, which can promote the adsorption of organic dyes and improve the transfer efficiency of the photocatalytic process.

•LaMn1 − xCoxO3/graphene (x = 0, 0.1, 0.15, 0.2) composites were synthesized via a sol–gel method and their photo catalytic activity was evaluated.•LaMn1 − xCoxO3 nanoparticles were successfully anchored on the surface of graphene and doping Co did not change the perovskite structure.•Doping Co enhances the photocatalytic performance of LaMnO3/graphene composites, and the mechanism was discussed.A novel photocatalyst of LaMn1 − xCoxO3/graphene composites had been synthesized by sol–gel process assisted with chelating effect of citric acid. The structure, morphology and valence state of prepared samples were characterized by thermogravimetry-differential thermal analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectra and UV–vis absorbance spectra. It was found that LaMnO3 perovskite phase was successfully processed which anchored on the surface of graphene sheets, and doping Co did not change the perovskite structure. The UV–vis photocatalytic activity of the photocatalysts was evaluated by the degradation of diamine green B. The results indicated that the photocatalytic activity of composites depend strongly on the doping content of Co. LaMn1 − xCoxO3/graphene composites prepared with x = 0.15 had the greatest photocatalytic activity, and it displayed good stability during the photocatalytic and recycling processes.The charge transfer mechanism that occurs in the LaMnO3/graphene composite during photocatalytic process is shown in the figure. During the photocatalysis reaction, three processes are crucial, which are: the adsorption of contaminant molecules, the light absorption, and the charge transportation and separation. Due to graphene's giant π-conjugation system and two-dimensional planar structure, the adsorptivity of dyes is improved compared to the bare LaMnO3. On the other hand, graphene can ensure holes and electron transfers quickly because of its high conductivity, and therefore, an effective charge separation can be achieved.

A novel photocatalyst of LaMnO3/graphene thin films with the perovskite-type was synthesized by sol-gel process assisted with spin-coating methods on glass substrates. The prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brumauer-Emmett-Teller (BET) surface area analyzer, X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. Results showed that after the introduction of graphene, the perovskite structure was unchanged and the size of LaMnO3 particles was about 22 nm, which uniformed growth in graphene sheet. Determination of contact angle indicated that the contact angle of glass substrate decreased and the hydrophilicity improved after treating with H2SO4 and APTES. The UV-Vis photocatalytic activity of the photocatalysts was evaluated by the degradation of diamine green B. LaMnO3/graphene thin films had better photocatalytic ability than LaMnO3 and TiO2 films. The obtained k was 0.5627 and 0.3441 h−1 corresponding to LaMnO3/graphene films and TiO2 films, respectively.FE-SEM image and HRTEM image of LaMnO3/graphene (The morphology of the LaMnO3/graphene composite is shown in the figure. It shows that the perovskite nanoparticles are grown on the graphene sheets. The insert drawing is the HRTEM image of LaMnO3/graphene, in which the light gray is graphene, and the black spots are the LaMnO3 nanoparticles. Due to graphene's two-dimensional planar structure, the adsorptivity of dyes is improved compared to the bare LaMnO3. Because of its high conductivity, graphene can ensure holes and electron transfers fastly. Therefore, an effective charge separation can be achieved)

•La1−xSrxMnO3/graphene thin films on glass substrate were obtained.•There was a combination of chemical bonds between thin films and the substrates.•LaMnO3/graphene thin film had sound stability and better photocatalytic ability than LaMnO3 thin film.•Doping Sr enhance the photocatalytic performance of the thin film.In this paper, La1−xSrxMnO3/graphene thin films were obtained using sol–gel and spin-coating methods on glass substrates. A combination of NN bonds was present between thin films and aminated glass substrates. The structure, grain size, and morphology were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectra. Results show that perovskite nanoparticles grew on graphene, and the size of the grain was about 40 nm. In the process of acid red 3GN photodegradation, LaMnO3/graphene thin film had sound stability and better photocatalytic ability than LaMnO3 thin film. A red shift of the absorption edge, which enhanced the photocatalytic performance of the LaMnO3/graphene thin film, was achieved by doping Sr. When x = 0.1, the de-coloration rate reached 94.52%, and the TOC concentration of acid red 3GN was only 0.36 mg/L after illumination 4 h.

•Silver decorated LaMnO3 nanorod/graphene composite were synthesized for the first time.•The ORR and OER of composite in alkaline medium were evaluated.•This composite as an efficient bifunctional catalyst has a good cycle performance.Perovskite LaMnO3 nanorod/reduced graphene oxides (LMO-NR/RGO) decorated with Ag nanoparticles are studied as a bifunctional catalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline electrolyte. LMO-NR/RGO composites are synthesized by using cetyltrimethyl ammonium bromide (CTAB) as template via a simple hydrothermal reaction followed by heat treatment; overlaying of Ag nanoparticles is obtained through a traditional silver mirror reaction. Electron microscopy reveals that LMO-NR is embedded between the sheets of RGO, and the material is homogeneously overlaid with Ag nanoparticles. The unique composite morphology of Ag/LMO-NR/RGO not only enhances the electron transport property by increasing conductivity but also facilitates the diffusion of electrolytes and oxygen. As confirmed by electrochemical testing, Ag/LMO-NR/RGO exhibits very strong synergy with Ag nanoparticles, LMO-NR, and RGO, and the catalytic activities of Ag/LMO-NR/RGO during ORR and OER are significantly improved. With the novel catalyst, the homemade zinc-air battery can be reversibly charged and discharged and display a stable cycle performance, indicating the great potential of this composite as an efficient bifunctional electrocatalyst for metal-air batteries.Silver decorated LaMnO3 nanorod/reduced graphene oxide composite possess excellent bifunctional electrocatalytic activity and good electrochemical stability in alkaline medium.