Theoretical And Experimental Studies On Adsorption And Photocatalysis Of Multi-component Titanate Semiconductor Materials

Recently,organic and synthetic dyes,which are widely used in industries,have deteriorated the aqueous environment and caused many issues in human health because of their not only teratogenic,toxic,and carcinogenic nature,but also difficulty in being decomposed as their chemical stability.However,organic dyes are becoming indispensable with the rapid development of industries related to their common application in coloring paper,cosmetics,and dyeing cotton and leather industries.Therefore,it is a global challenge to research quick and complete removal strategies for organic pollutants from wastewater.Titanium dioxide(TiO₂)semiconductor has been widely investigated because of its long-term chemical stability,high catalytic activity,nontoxicity,strong optical absorption,low cost,and excellent band alignment to many oxidation reductions.Many researchers focus on TiO₂ nanoparticles for their outstanding performance in photocatalysis,hydrogen production,chemical sensors,sensitized solar cells,and adsorbents due to the large surface area.However,the TiO₂ photoelectrochemical efficiency is limited by some factors,such as large band gap and low charge carrier transfer.Especially,the TiO₂ wide band gap limits its light-harvesting capability to the visible light range,wasting about 95%of the solar light energy.This puts forward a challenge to develop new materials with small band gap relative to TiO₂ to utilize most sunlight energy:(1)Advanced adsorbents need high adsorption rate and superior adsorption capability to clean up organic methylene blue(MB)from wastewater.We prepared K₂Ti₈O₁₇ nanowires grown along the[0 1 0]direction with a one-step hydrothermal method.The K₂Ti₈O₁₇ nanowires with tens of nanometers in diameter and tens of micrometers in length were achieved with smooth surfaces and twisted wire-like morphology.The K₂Ti₈O₁₇ nanowires exhibit high uptake capacity of 208.8 mg·g-1 in the MB removal under equilibrium pH=7.The adsorption equilibrium of MB onto the K₂Ti₈O₁₇ adsorbent is achieved with a 97%removal rate of MB within only 21 min,which is the shortest adsorption time among the recently reported inorganic adsorbents toward MB.The adsorption process has a good agreement with the well-known pseudo-second-order kinetic model and the Langmuir isotherm model.Fourier transform infrared measurements suggest that the adsorption can be assigned to the hydrogen bonding and electrostatic attraction between MB and K₂Ti₈O₁₇.This ultrafast removal ability is due to the larger(0 2 0)interplanar spacing and zigzag surface structure of the nanowires,which provides abundant active adsorption sites.Thermodynamic parameters reflect the spontaneous,exothermic,and feasible uptake of MB.This work highlights the great significance of K₂Ti₈O₁₇ nanowires as a low-cost promising material used for the adsorptive elimination of organic contaminations in fast water purification on a large scale.(2)New-type of layered K_0.8Ni_0.4Ti_1.6O₄(KNTO)nanosheets were synthesized over 80 min with 3 M KOH at 320? by a simple hydrothermal way for the first time.KNTO single crystal nanosheets with bamboo leaflike shape were confirmed by HRTEM.For KNTO semiconductor,double absorption with band gaps of 1.88 and 2.08 eV are demonstrated by the UV-vis diffuse reflectance spectra.KNTO not only exhibits adsorption ability on MB in black environment,but also possesses good photodegradation capacity for MB.The trapping experiments manifested that photogenerated holes are the primary active species in the process of MB photodegradation.This work highlights the potential multifunctional materials for removing contaminants from waste.(3)Novel multifeatured hollandite K(1.46)Fe(0.8)Ti(7.2)O₁₆(KFTO)was synthesized by a simple hydrothermal method.Magnetic KFTO microrods were well controlled to long rectangular rods with pyramid-shaped tops.A KFTO growth mechanism was proposed based on examining phase and morphology of the samples acquired at different reaction times.The KFTO morphology was confirmed by the calculated surface energies.The UVvis diffuse reflectance spectra of KFTO microrods showed double absorption with band gaps of 2.01 and 2.16 eV,which was further confirmed by photoluminescence.Firstprinciples studies revealed that the double absorption and magnetic properties originate from the d-d transitions of Fe³+ under the crystal field.The magnetic property could be applied in ferromagnetic semiconductor devices and the double absorption could be applied in visible-light harvesting.This work highlights the multifunctional KFTO microrods with low cost and environmental friendliness.