Modification of MoS2/GO composites with ball milling and thermal treatment for catalytic application

Hydrogen production can be outlined as an important aspect of the modern economy. In order to be more clean and renewable, green hydrogen is most desirable, where expensive catalysts for water electrolysis are usually used. As alternative, transition metal dichalcogenides represent potentially good material, with room for further improvement. Molybdenum disulfide is a stable material with a reasonable amount of it available. The properties of the material can be easily tuned in order to increase its charge transport and create more active sites. The incorporation of defects and additives can be beneficial for the catalytic activity of MoS2. Graphene oxide (GO) is carbon nanomaterial, with a large surface area and when reduced, it could be used as a conductive additive. Furthermore, ball milling is a known low-cost, simple and scalable method to introduce defects in the structure. Therefore, combining these two approaches should result in a material with enhanced catalytic activity for hydrogen evolution reaction. The molybdenum disulfide was prepared by easy one-step hydrothermal synthesis. The graphene oxide was first obtained by modified Hummers’ method and after that reduced by thermal treatment at 200 °C. Thus prepared constituents are combined in different mass ratios and composites were obtained by milling with a high-energy ball mill. The various milling parameters were optimized. The prepared composites were analyzed as catalysts for hydrogen evolution reaction in an acidic solution

Graphene oxide/12 tungstophosphoric acid nanocomposites – achieving favorable properties with ion beams for electrochemical supercapacitors

In recent years graphene oxide (GO)/12-tungstophosphoric acid (WPA) nanocomposites have demonstrated promising potential for electrochemical supercapacitors. However, to enhance their performance, it is necessary to modify the surface chemistry of GO to minimize the influence of basal plane oxygen groups, which hinder the material's conductivity. Additionally, some degree of structural modification of WPA is desired. In this regard, ion beam irradiation presents a promising method to simultaneously optimize surface chemistry of GO and structurally modify WPA. To accomplish this, ion beam irradiation is employed for modification of individual components as well as their nanocomposites with varying mass ratios. Different ion species, fluences and energies were utilized depending on the sample type, ranging from 10 keV C to 710 MeV Bi. Spectroscopy methods were employed to gain insight into the type and degree of structural modification in WPA. A direct correlation is observed between the parameters of the ion beams and the resulting structural changes. As the disordering increases, the structure transitions from partially modified to increased bond breaking, ultimately leading to reconnected bronze-like structures. By increasing the fluence, a gradual modification of the structure and surface chemistry of GO was possible. The effects of irradiation on GO and WPA are particularly pronounced in irradiated composites, where higher capacitance is measured

Ion-beam irradiated graphene oxide, 12-tungstophosphoric acid and their nanocomposites for electrochemical supercapacitors

Ion beam modification of materials is notable method for achieving their unique structural, electronic, and other physicochemical properties. In the case of graphene oxide (GO) such modification of structure and surface chemistry is known to yield properties interesting for electrochemical supercapacitors. The performance of GO supercapacitors can be additionally improved by incorporating components with attractive redox properties. In this work, the influence of ion beam irradiation on synergy of GO and 12-tungstophosphoric acid (WPA) in their nanocomposite was investigated. For that, both components and their composites with different mass ratios were irradiated using different ion species, fluences and energies (from 10 keV C to 710 MeV Bi). For the irradiated WPA, results showed clear correlation between ion beam parameters, degree of structural modification and electrochemical properties. With increasing structural modification, bond breaking is first induced giving higher catalytic activity toward HER. Further irradiation resulted in an increased interconnection of polytungstate species producing lower catalytic activity and lower lithiation capacity. Irradiated GO showed modified surface chemistry, with preferable reduction of alkoxy and epoxy groups, changes in morphology and electric properties due to increased number of defects with increasing fluence, synergic effect of ion beam irradiated GO and WPA resulted in higher capacitance of irradiated composites compared to GO presumably because of interaction of structurally modified WPA with defect sites on GO thus reducing electrolyte flow along ion tracks

Ion-beam irradiated graphene oxide, 12-tungstophosphoric acid and their nanocomposites for electrochemical supercapacitors

Ion beam modification of materials is notable method for achieving their unique structural, electronic, and other physicochemical properties. In the case of graphene oxide (GO) such modification of structure and surface chemistry is known to yield properties interesting for electrochemical supercapacitors. The performance of GO supercapacitors can be additionally improved by incorporating components with attractive redox properties. In this work, the influence of ion beam irradiation on synergy of GO and 12-tungstophosphoric acid (WPA) in their nanocomposite was investigated. For that, both components and their composites with different mass ratios were irradiated using different ion species, fluences and energies (from 10 keV C to 710 MeV Bi). For the irradiated WPA, results showed clear correlation between ion beam parameters, degree of structural modification and electrochemical properties. With increasing structural modification, bond breaking is first induced giving higher catalytic activity toward HER. Further irradiation resulted in an increased interconnection of polytungstate species producing lower catalytic activity and lower lithiation capacity. Irradiated GO showed modified surface chemistry, with preferable reduction of alkoxy and epoxy groups, changes in morphology and electric properties due to increased number of defects with increasing fluence, synergic effect of ion beam irradiated GO and WPA resulted in higher capacitance of irradiated composites compared to GO presumably because of interaction of structurally modified WPA with defect sites on GO thus reducing electrolyte flow along ion tracks

Graphene oxide/12 tungstophosphoric acid nanocomposites – achieving favorable properties with ion beams for electrochemical supercapacitors

In recent years graphene oxide (GO)/12-tungstophosphoric acid (WPA) nanocomposites have demonstrated promising potential for electrochemical supercapacitors. However, to enhance their performance, it is necessary to modify the surface chemistry of GO to minimize the influence of basal plane oxygen groups, which hinder the material's conductivity. Additionally, some degree of structural modification of WPA is desired. In this regard, ion beam irradiation presents a promising method to simultaneously optimize surface chemistry of GO and structurally modify WPA. To accomplish this, ion beam irradiation is employed for modification of individual components as well as their nanocomposites with varying mass ratios. Different ion species, fluences and energies were utilized depending on the sample type, ranging from 10 keV C to 710 MeV Bi. Spectroscopy methods were employed to gain insight into the type and degree of structural modification in WPA. A direct correlation is observed between the parameters of the ion beams and the resulting structural changes. As the disordering increases, the structure transitions from partially modified to increased bond breaking, ultimately leading to reconnected bronze-like structures. By increasing the fluence, a gradual modification of the structure and surface chemistry of GO was possible. The effects of irradiation on GO and WPA are particularly pronounced in irradiated composites, where higher capacitance is measured

SYNTHESIS OF COMPOSITE NANOPARTICLES USING COATING OF THE CORE NANOPARTICLES WITH SPINEL FERRITES LAYERS

Pri diplomskem delu smo raziskovali postopek sinteze kompozitnih nanodelcev, kjer smo različne jedrne nanodelce (silicijev dioksid – SiO2 in barijev heksaferit – BaFe12O19) prevlekli s plastjo spinelnega ferita. Plast spinelnega ferita je nastala s soobarjanjem Fe3+/M2+ ionov (M2+ = Fe2+, Co2+) ter heterogeno nukleacijo trdnega produkta na površino jedrnih nanodelcev. Sintezo kompozitnih nanodelcev prekritih s plastjo kobaltovega ferita smo naredili s stehiometričnim razmerjem Fe3+/Co2+ ionov in povečano koncentracijo Co2+ ionov. Z izbrano metodo smo na površino jedrnih nanodelcev nukleirali plast spinelnega ferita (maghemit ali kobaltov ferit). Plast kobaltovega ferita ni imela stehiometrične sestave. Pri sintezi kompozitnih nanodelcev, kjer smo kot jedrne nanodelce uporabili nanodelce barijevega heksaferita velikosti 5 − 70 nm, smo dobili nehomogen vzorec. Vzorec je vseboval majhne nanodelce (13 nm), pri katerih so oborjeni ioni zreagirali z jedrnimi nanodelci ter večje kompozitne nanodelce, kjer je bila spinelna plast heterogeno nukleirana na bazalnih površinah ploščatih heksaferitnih nanodelcev. Pri pripravi kompozitnih nanodelcev, kjer smo heksaferitne nanodelce prevlekli s plastjo kobaltovega ferita, smo v primeru stehiometrične in povečane koncetacije Co2+ ionov dobili nestehiometrično sestavo spinelne pasti na površini jedrnih nanodelcev. Magnetne meritve so pokazale, da se je nasičena magnetizacija v primeru kompozitov s spinelno plastjo maghemita povečala, kakor se je povečala tudi remanenca. Pri kompozitih s plastjo kobaltovega ferita na površini se je zmanjševala tako nasičena magnetizacija kot koercitivnost.The preparation of the composite nanoparticles using coating of different core nanoparticles (silicion dioxide – SiO2 or barium hexaferrite - BaFe12O19) with thin layer of spinel ferrites was studied. The spinel layer was formed by a heterogeneous nucleation of the solid phase on the surfaces of the core nanoparticle during co-precipitation of the Fe3+/M2+ ions (M2+= Fe2+, Co2+). The stoichiometric ratio of Fe3+/Co2+ ions and an increased concentration of Co2+ ions were used for the synthesis of the composite nanoparticles with the cobalt ferrite layer. With selected method we managed to synthesize the composite nanoparticles with the thin layer of spinel (maghemite and cobalt ferrite) on the SiO2 core nanoparticles, however the cobalt-ferrite layer didn’t have the stoichiometric composition. With synthesis of the composite nanoparticles, where we used barium-hexaferrite nanoparticles (diameter 5 − 70 nm) as the cores, a nonhomogeneous product was obtained. The synthesised product consisted of small composite nanoparticles (13 nm) where the precipitated ions reacted with the core nanoparticles resulting in new compound, and of the larger composite nanoparticles that had the spinel layer located on the basal planes of the hexaferrite platelet cores. When the cobalt-ferrite layer was coated onto the barium-hexaferrite nanoparticles, the product was similar than on the SiO2 core nanoparticles - a thin layer of cobalt ferrite had the nonstoichiometric composition. With magnetic measurement we discovered, that saturated magnetization and remanence increased for the composite nanoparticles with maghemite layer compared to the hexaferrite core nanoparticles. For the composite nanoparticles with the cobalt-ferrite layer, the saturated magnetization and coercivity decreased compared to the hexaferrite cores