M.S. Ata

A review of new methods of surface chemical modification, dispersion and electrophoretic deposition of metal oxide particles

A bio-inspired chemical approach has been developed for the surface modification, dispersion and electrophoretic deposition (EPD) of metal oxide particles. The study of the chemical mechanism of mussel adhesion to different surfaces has driven the development of advanced dispersing agents with strong adsorption to oxide nanoparticles. The investigation of dopamine, caffeic acid, tiron and other molecules from the catechol family, and various molecules from salicylic acid, gallic acid, and chromotropic acid families revealed their strong adsorption to metal oxide surfaces. The analysis of dispersion and deposition yield data for various materials provided an insight into the influence of molecular structures of the organic dispersants on adsorption mechanisms and EPD efficiency. The adsorbed dispersants imparted new and unique properties to the nanoparticles. Further advancements in the EPD technology were achieved by the use of cationic and anionic dyes such as pyrocatechol violet, celestine blue, alizarin red from the catechol family and alizarin yellow, aurintricarboxylic acid and calconcarboxylic acid from salicylate family and their derivatives. It was discovered that polyaromatic dyes can be used as efficient co-dispersants for oxide materials, carbon nanotubes and graphene for the fabrication of composite films by EPD. Another important breakthrough was the development of film forming dispersants for EPD nanotechnology. New strategies have emerged for the synthesis of non-agglomerated nanoparticles of controlled size, organic fibers and coated particles. The use of new dispersants with strong interfacial adsorption and multifunctional properties has driven the development of advanced composites, containing metal oxide nanoparticles, conductive polymers, carbon nanotubes, graphene, polyelectrolytes and other materials. Colloidal and interface chemistry of new dispersing agents is emerging as a new area of technological and scientific interest.

Electrophoretic deposition of TiO2 nanoparticles using organic dyes

Electrophoretic deposition method has been developed for the deposition of TiO(2) nanoparticles modified with organic dyes. Alizarin red, alizarin yellow and pyrocatechol violet dyes were used for the dispersion and charging of TiO(2) in ethanol and anodic electrophoretic deposition of TiO(2) films. The deposition yield was varied by the variation of dye concentration in suspensions and deposition time. Aurintricarboxylic acid dye was used for the deposition of TiO(2) from aqueous suspensions. It was found that thin films of pure aurintricarboxylic acid and composite aurintricarboxylic acid TiO(2) films can be obtained. The deposition yield was studied by quartz crystal microbalance. Dye film thickness was varied in the range of 0.1-2 μm by variation in the deposition time at a constant voltage. The composition of the films and the amount of the deposited material can be varied by the variation of TiO(2) and dye concentration in suspensions and deposition time. The films were studied by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential thermal analysis and electron microscopy. The deposition mechanisms were discussed. The electrophoretic deposition method offers advantages for the fabrication of dye-sensitized TiO(2) films.

Colloidal methods for the fabrication of carbon nanotube-manganese dioxide and carbon nanotube-polypyrrole composites using bile acids.

Nature inspired strategies have been developed for the colloidal processing of advanced composites for supercapacitor applications. New approach was based on the use of commercially available bile acid salts, such as sodium cholate (ChNa) and taurocholic acid sodium salt (TChNa). It was demonstrated that cholic acid (ChH) films can be obtained by electrophoretic deposition (EPD) from ChNa solutions. The analysis of deposition yield, quartz crystal microbalance and cyclic voltammetry data provided an insight into the anodic deposition mechanism. The outstanding suspension stability of multiwalled carbon nanotubes (MWCNT), achieved using bile acids as anionic dispersants, allowed the fabrication of MWCNT films by EPD. The use of ChNa for EPD offered advantages of binding and film forming properties of this material. Composite MnO2-MWCNT films, prepared using ChNa as a dispersant and film forming agent for EPD, showed promising capacitive behavior. In another colloidal strategy, TChNa was used as a dispersant for MWCNT for the fabrication of polypyrrole (PPy) coated MWCNT. The use of PPy coated MWCNT allowed the fabrication of electrodes with high active mass loading, high capacitance and excellent capacitance retention at high charge-discharge rates.

Universal dispersing agent for electrophoretic deposition of inorganic materials with improved adsorption, triggered by chelating monomers

Poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) is a polymeric functional material with a number of unique physical properties, which attracted significant interest of different scientific communities. Films of PAZO were deposited by anodic electrophoretic deposition (EPD) under constant current and constant voltage conditions. The deposition kinetics was analyzed under different conditions and the deposition mechanism was discussed. New strategy was developed for the EPD of different inorganic materials and composites using PAZO as a dispersing, charging, binding and film forming agent. It was found that PAZO exhibits remarkable adsorption on various inorganic materials due to the presence of chelating salicylate ligands in its molecular structure. The salicylate ligands of PAZO monomers provide multiple adsorption sites by complexation of metal atoms on particle surfaces and allow for efficient electrosteric stabilization of particle suspensions. The remarkable performance of PAZO in its application in EPD have been exemplified by deposition of a wide variety of inorganic materials including the single element oxides (NiO, ZnO, Fe2O3) the complex oxides (Al2TiO5, BaTiO3, ZrSiO4, CoFe2O4) different nitrides (TiN, Si3N4, BN) as well as pure Ni metal and hydrotalcite clay. The use of PAZO can avoid limitation of other dispersing agents in deposition and co-deposition of different materials. Composite films were obtained using PAZO as a co-dispersant for different inorganic materials. The deposit composition, microstructure and deposition yield can be varied. The EPD method offers the advantages of simplicity, high deposition rate, and ability to deposit thin or thick films.

Strategies for liquid-liquid extraction of oxide particles for applications in supercapacitor electrodes and thin films

Bottom-up and top-down liquid-liquid extraction methods have been developed for the transfer of colloidal metal oxide particles, synthesized in an aqueous phase, to organic phases. In such methods the agglomeration of the particles during the drying stage was avoided. Hexadecylamine was used as an extractor for MnO2 particles in the bottom-up extraction to the 1-butanol phase and top-down extraction to the dichloromethane phase. The reduction of particle agglomeration facilitated the fabrication of MnO2-carbon nanotube composite electrodes for electrochemical supercapacitors with enhanced mixing of the individual components and active mass as high as 35mgcm-2. Electrochemical testing results showed superior performance of the composite MnO2-carbon nanotube electrodes, prepared by the bottom-up strategy. The new strategies allowed the fabrication of advanced electrodes, which showed a capacitance of 5.48Fcm-2 at a scan rate of 2mVs-1, good capacitance retention at high scan rates and low resistance. In another conceptually new bottom-up strategy colloidal titania particles were modified during synthesis with 2,3,4-trihydroxybenzaldehyde, which allowed strong catecholate-type bonding to the Ti atoms on the particle surface. The Schiff base reaction with hexadecylamine at the liquid-liquid interface allowed for particle extraction. The extraction strategies developed in this investigation pave the way for agglomerate-free processing of advanced films, coatings and devices by colloidal methods.

Electrophoretic deposition of linear polyethylenimine and composite films

Abstract Electrophoretic deposition method has been developed for the electrodeposition of linear polyethylenimine (LPEI) films. The deposition mechanism is based on the electrophoresis of protonated LPEI-H+, base generation at the cathode surface, charge neutralisation and formation of insoluble LPEI films. Quartz crystal microbalance data, coupled with the results of electron microscopy, showed that deposition rate and film thickness can be varied and controlled by the variation of deposition time and voltage. LPEI films provided corrosion protection of stainless steel substrates. LPEI was used for the dispersion, charging and electrophoretic deposition of TiO2, hydrotalcite and MnO2 particles and fabrication of composite films. Scanning electron microscopy and thermogravimetric analysis showed the formation of composite films, containing 45·4%TiO2, 53·1% hydrotalcite and 33·3%MnO2 in the LPEI matrix. The film thickness was varied in the range of 0·1–4 μm by variation of the deposition time at a constant deposition voltage. The proposed approach paves the way for the fabrication of organic–inorganic composite films combining functional properties of LPEI and inorganic materials.

Fabrication of Mn3O4–carbon nanotube composites with high areal capacitance using cationic and anionic dispersants

Mn3O4-multiwalled carbon nanotube (MWCNT) electrodes for supercapacitors with high active mass loadings have been fabricated with the goal of achieving a high area normalized capacitance (CS) and enhanced capacitance retention at high charge-discharge rates. Poly(4-styrenesulfonic acid-co-maleic acid) sodium salt P(SSA-MA) was used as a charging and dispersing agent for the fabrication of Mn3O4. The unique bonding properties of the MA monomers allowed efficient P(SSA-MA) adsorption on Mn3O4, whereas SSA monomers imparted a negative charge. Cationic ethyl violet (EV) and pyronin Y (PY) dyes were used for dispersion and charging of MWCNT. Good dispersion of the individual components and their electrostatic heterocoagulation facilitated efficient mixing, which allowed enhanced capacitive behavior at mass loadings of 28.4 mg cm-2, which meet requirements for practical applications. The highest capacitance of 2.8 F cm-2 was obtained at a scan rate of 2 mV s-1 for the composites, prepared using PY. However, the composites, prepared using EV showed better capacitance retention of 88% in the scan rate range of 2-100 mV s-1 and the capacitance of 2.1 F cm-2 was obtained at a scan rate of 100 mV s-1. The composites showed activation behavior during cycling, which resulted in a capacitance increase and electrical resistance reduction. The results of this investigation showed that Mn3O4-MWCNT composites, prepared by new colloidal methods are promising materials for practical applications in electrochemical supercapacitors.