Laser-induced Synthesis Of Metallic Nanocomposites And Applications

Nanomaterials and nanotechnologies are experiencing tremendous development in 21th century,which not only promotes the progress of basic science as physics,chemical,material,but also some interdisciplinary technologies as bio-pharmaceutical,environmental monitoring and energy storage.The widespread usage of nanomaterials is playing an important part in people’s daily lives,and increasing demands for new functional nanomaterials impact the development of synthetic technology.Laser-induced synthesis is one of the most advanced synthesis technology,which is a perfect combination of nanotechnology and impulse laser.With the improvement of pulsed laser quality in the past decades,the application laser-induced synthetic technique becomes more mature.This technique shows many advantages such as environmental-friendly,easy for operation and so on.Abundant attentions have been attracted on this synthesis technique,and the rapid development makes it possible for practical application.Based on laser-induced synthesis technique,we synthesized various of metallic oxide and metal sulfide nanocomposites,which can be served as nano-adsorbent for organic dyes and heavy metal ions in waste water;we synthesized noble metal nanospheres/nanocomposites without any surfactant or stabilizer,and investigated their electrochemical catalytic activities for methanol oxidation reaction in direct methanol fuel cells.We design a simple and versatile strategy to synthesize CuO/Cu2O nanoporous materials by laser irradiation of CuO powders in distilled water without any additive reagents.The morphologies of the nanocomposites are rice-shaped architectures with abundant pores(4-8 nm),the length and diameter of the nanomaterials are about 100 nm and 50 nm,respectively.Compared with commercial CuO powders(120-200 nm),the laser irradiation process apparently reduced particle size,and induced rough and rugged structures on its surface.The laser beam energy is absorbed by nanomaterials and eventually transform into heat,which enables the exposed surfaces of the initial CuO structures to be local-melted in solution.Compared to Cu metal elements,the O species will be more easily to be removed/escaped from original structures.Meanwhile,the recrystallizations of residual Cu and O species in original region will take place during pulse laser irradiation,resulting in the formation of porous Cu2O@CuO nanocomposites.The nanoporous induced by laser irradiation apparently increase the specific surface area of nanomaterials,and meanwhile,abundant hydroxyl(-OH)groups can also be generated on the nanoporous surface,which provide amount of activity site for adsorption.No organic surfactant or stabilizer was used in synthesis process,which guarantee the purity of the CuO/Cu2O nanomaterials.The porous Cu2O@CuO nanocomposites exhibit excellent adsorption performances for the removal of organic dye molecules from wastewater.Our measurements indicate that 99.69%MB molecules(80mg/L,3mL)can be removed from the solution via the 1.8 mg Cu2O@CuO nanocomposites after 1 min,while 95.63%of MB molecules were adsorbed with about 200 mg un-irradiated CuO powders in the same reaction time.In addition,the equilibrium adsorption capacity of CuO/Cu2O nanocomposites reach about 2396 mg/g,which is 7.46 times of the commercial CuO powders(321 mg/g).This CuO/Cu2O adsorbent can also adsorb many other organic dyes such as methyl orange(MO)or rhodamine 6G(R6G),and it is also very efficient in adsorption process.Our results have opened up a novel green paradigm to obtain pure and highly porous CuO/Cu2O nanocomposites,demonstrating excellent absorption performance in the removal of organic dyes pollution from wastewater.The adsorbent based on nanomaterials is a wise choice for removing dye molecules and heavy-metal ions pollutants in waste water.However,there is an obvious weakness in adsorption treatment.In most cases,the nano-adsorbents will inevitably suspended in the solution after adsorption process,which result in anthropogenic secondary pollution once again.The subsequent removal of nano-adsorbents remains a serious challenge for wastewater purification.Thus,we synthesized fibrous-shaped CuO/CuS nanoporous structures through pulsed laser irradiation of CuO powders in sodium sulfide liquid,which exhibits unique adsorption performance and can avoid the adsorbent separation process.The fibrous architectures is constitute by numerous cross-linked nanochains(diameter～6 nm),with abundant pores(～2 nm)on the surface,which obviously enhanced specific surface area of materials.The laser beam energy can be absorbed by CuO nanomaterials and make it local-melted/evaporated on the surface,and abundant oxygen species are removed in this process;the excited cuprum species will recrystallized with S ions in solution and suffered ultra-rapid acid etching process at the same time,finally forming fibrous-shaped CuO/CuS nanoporous structures.Laser irradiation process can also induce oxygen and sulfur vacancies defects and provide a positive charged surface state for CuO/CuS nanocomposites,which is very essential for the adsorption of negatively charged contaminants from waste water.After electrostatic adsorption process between adsorbent and contaminants in solution,the novel CuO/CuS adsorbent can be aggregated/agglomerated together and completely self-deposited on the bottom of the solution.The adsorption experiment show that MB solution(50 mg/L,10 mL)and K2Cr2O7 solution(5×10-4 mol/L,10 mL)were adsorbed by 5 mg fibrous-shaped CuO/CuS nanoporous materials,and the adsorption/self-deposition process were accomplished after 7 hours and 20 minutes for MB and K2Cr2O7,respectively.So with this nano-adsorbent,there is no additional process for adsorbent separation after adsorption treatment,which is significant for the wastewater purification.This achievement has been reported as "spotlight on optics" by OSA(The Optical Society)in Opt.Mater.Express,The direct methanol fuel cell(DMFC)is one of most optimal candidates in the future,which shows its advantages on aspects of environmental friendly,cost-efficient and convenient.But at the present stage,catalyst for methanol oxidation reaction(MOR)is still a limitation for its practical application.Noble-metal platinum and platinum-based materials have been illustrated as a promising catalyst in direct methanol fuel cells for its superior catalytic property.But in most of previous works,it is mainly concentrate on synthesis of Pt based nanostructures with specific morphologies via sophisticated chemical reactions(etching,reducing and oxidation)by utilizing abundant of complex polymer stabilizers,surfactants and other organic auxiliary reagents such as polyvinyl pyrrolidone(PVP)and cetyl trimethyl ammonium bromide(CTAB).However,the residual additives are very hard to remove by centrifugation,thermal annealing,plasma cleaning and other cleaning and purifying process.The inevitable residual additives may adhere on the surface of nanocatalyst,especially porous and fibrous structures,and result in negative influences to its catalytic activity.In this work,through 1064 um pulsed laser ablation of Pt target in distilled water,we synthesized pure platinum nanospheres with diameters about 15-22 nm.Without any organic reagents in the fabrication process,the Pt nanospheres with clear surface show enhanced catalytic activity in MOR process.For comparison,we synthesized platinum nanospheres with surfactant PVP and CTAB,respectively;although we performed conventional cleaning process afterwards,the existence of surfactant is still detected.The electrochemistry experiments were performed with the three group of samples.Results show that electrochemically active surface area(ECSA)of pure platinum nanospheres are 7.5 and 14.8 times higher than Pt/PVP and Pt/CTAB samples;and the peak mass current in MOR process are 610 and 1050 times than Pt/PVP and Pt/CTAB samples,respectively.The comparison demonstrates that residual surfactant will obstruct the contact between catalyst and solution,reduce electron transmission efficiency in catalytic process,which can be significantly reduce catalytic activity and even prevent the MOR process.So laser-induced synthesis of Pt nanomaterials can avoid the usage of organic regent,and the nanocatalyst shows enhanced catalytic activity.To fturther promoting the poison-resistance of the catalyst,we synthesized the spherical Pt/Pd nanocomposite through laser ablation Pt target in Na2PdCl4 solution.The Pt/Pd nanocomposite not only shows similar catalytic activity as pure Pt spheres,but also exhibit excellent poison-resistance property in MOR process,and finally provide an excellent catalyst for facilitating of future fuel cells applications.Optical waveguide structure is a basic component in integrated optics field.The light wave can be restricted in waveguide region by total reflection,which will effectively improve the light intensity when propagation in the waveguide.The waveguide structure were fabricated by 6.0 MeV oxygen ion irradiation on Ca0.4Ba0.6Nb2O6(CBN-40)and 6.0 MeV carbon ion irradiation on Ce:Lu2SiO5(Ce:LSO)crystals.After ion irradiation process,the nsur(surface refractive index)of CBN-40 waveguide is decreased in TE polarization direction,indicating a "barrier"type waveguide was formed;while Insur is increased in TM polarization direction,showing a typical "well"+"barrier" type waveguide.And for Ce:LSO crystal,ion irradiation also induced a "well"+"barrier?" type waveguide in the TM polarization direction.Moreover,the fluorescence intensity of Ce:LSO crystal is obviously increased,the reason is that electrons are transmitted from carbon ions to cerium ions after ion irradiation process.This novel property will apparently promote the Ce:LSO waveguide application in many conditions.