Yangshuai Liu

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.

Surface modification of MnO2 and carbon nanotubes using organic dyes for nanotechnology of electrochemical supercapacitors

Efficient dispersion and electrophoretic deposition (EPD) of multiwalled carbon nanotubes (MWCNTs) was achieved using organic dyes, such as pyrocatechol violet (PV) and m-cresol purple (CP). The problem of MnO2 nanoparticle dispersion in concentrated suspensions was addressed by the use of PV as a dispersant. The analysis and comparison of experimental data for PV and CP provided insight into the influence of chemical structures of the dyes on their adsorption on MWCNTs and MnO2. The adsorption of PV on MWCNTs and MnO2 was attributed to π–π interactions and catecholate type bonding, respectively. The EPD yield can be varied by the variation of the PV concentration in the suspensions, deposition voltage and time. It was found that PV can be used as a co-dispersant for EPD of MWCNTs and MnO2 and the fabrication of MnO2–MWCNT composites. The proposed approach offers advantages of uniform distribution of individual components and low binder content in the composite. MnO2–MWCNT films were prepared by EPD for thin film electrodes of electrochemical supercapacitors (ES). Bulk MnO2–MWCNT electrodes with a material loading of 40 mg cm−2 were obtained by the impregnation of Ni foam current collectors. The highest specific capacitance of 5.9 F cm−2 (148 F g−1) was achieved. The composite materials are promising for ES applications.

Azopolymer triggered electrophoretic deposition of MnO2-carbon nanotube composites and polypyrrole coated carbon nanotubes for supercapacitors

Poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) exhibits a number of unique physical properties, which are important for diverse applications of this functional polymer in photonics, optoelectronics, memory devices and sensors. A conceptually new strategy has been utilized for the fabrication of thin films of PAZO using electrophoretic deposition (EPD). The deposition kinetics and mechanism have been investigated and the advantages of EPD have been discussed. Our new findings in the surface and interface chemistry allowed for the development of surface modification methods, which were utilized for the electrosteric dispersion and EPD of MnO2 nanofibers, multiwalled carbon nanotubes (MWCNT), polypyrrole (PPy) nanoparticles and PPy coated MWCNT. New method has been developed for the fabrication of PPy coated MWCNT, using bromothymol blue sodium salt as a dopant for PPy and dispersant for MWCNT. The aromatic PAZO monomers, containing chelating salicylate ligands provided multiple adsorption sites for PAZO adsorption on different materials and allowed for their efficient electrosteric dispersion. Another major finding was the possibility of efficient deposition of composites, using PAZO as a co-dispersant for MnO2 nanofibers and MWCNT. The MnO2 nanofibers, MWCNT, PPy nanoparticles, PPy coated MWCNT and composites, deposited by EPD, were used for energy storage in electrodes of electrochemical supercapacitors. Testing results showed beneficial effect of PAZO for the dispersion and EPD of advanced supercapacitor materials. The results of this investigation paved the way for EPD of other composites utilizing properties of different functional materials and unique physical properties of PAZO.

Aqueous electrostatic dispersion and heterocoagulation of multiwalled carbon nanotubes and manganese dioxide for the fabrication of supercapacitor electrodes and devices

A conceptually new approach has been developed for the fabrication of MnO2-multiwalled carbon nanotube (MWCNT) composites for electrodes of electrochemical supercapacitors (ES). Benzyldimethylhexadecylammonium chloride (BAC) surfactant and caffeic acid (CA) selectively adsorbed on MWCNT and MnO2, respectively, and allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged MnO2. The comparison of the electrophoretic deposition yield data for BAC, CA and other molecules provided an insight into the influence of the molecular structure on adsorption of the molecules and dispersion of MWCNT and MnO2. Advanced composite materials with good mixing of the individual components were obtained by heterocoagulation, based on an ion-pairing assembly of BAC and CA. The composite electrodes, prepared by the new method showed superior electrochemical performance. It was found that high capacitance and good capacitance retention at high charge–discharge rates can be achieved at high active mass loadings. A practical outcome of this study was the fabrication of an asymmetric SC device, containing a positive MnO2–MWCNT electrode and negative activated carbon–carbon black composite electrode with a voltage window of 1.8 V in an aqueous electrolyte. The asymmetric device showed high capacitance, high power-energy characteristics, good capacitance retention at high charge–discharge rates and cyclic stability.

Surface modification and cathodic electrophoretic deposition of ceramic materials and composites using celestine blue dye

A new method has been developed for the surface modification of inorganic particles, which allowed their efficient electrostatic dispersion and cathodic electrophoretic deposition (EPD). The approach is based on the use of cationic celestine blue (CB) dye as a charging and dispersing agent. The key advantages of this approach are related to its applicability to different materials and strong adsorption of CB to the inorganic surfaces, which is of critical importance for efficient particle dispersion. Proof-of-concept studies involved the EPD of thin films of various materials, such as TiO2, MnO2, Mn3O4, BaTiO3, halloysite nanotubes, zirconia and yttria. The results of the deposition rate measurements, Fourier transform infrared spectroscopy, UV-vis and quartz crystal microbalance studies provided an insight into the mechanism of CB adsorption, which involved the interactions of the OH groups of the catechol ligand of CB and metal atoms on the particle surface. It was demonstrated that CB can be used as an efficient dispersing agent for the nanoparticle synthesis by chemical precipitation methods. The feasibility of EPD of various oxide materials paved the way to the EPD of various composites using CB as a co-dispersant for the individual components. Thin films of individual oxides and composites were investigated by electron microscopy and X-ray diffraction methods. The benefits of cathodic EPD for nanotechnology were demonstrated by the formation of nanostructured MnO2 films on commercial high surface area current collectors for energy storage in electrochemical supercapacitors. Testing results showed that the method allowed the fabrication of efficient electrodes with high capacitance and excellent capacitance retention at high charge–discharge rates. The new method paves the way for the deposition of other functional materials and composites for advanced applications.

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.