Self-assembly And Photocatalytic Properties Of The Exposed Crystal Surface-controlled Rutile TiO₂Nanorods

In this paper, the exposed crystal surface-controlled rutile TiO2nanorodmicrospheres were synthesized via hydrothermal treatment using tetrabutyl titanate withcetyltrimethylammonium bromide aggregates as a structure-directing agent and NaCl asa morphology modifier. Prepared samples were characterized by X-ray diffraction(XRD), raman spectra, transmission electron microscopy (TEM), high-resolutiontransmission electron microscopy (HRTEM), field-emission scanning electronmicroscopy (FESEM), and N2adsorption-desorption isotherms. The results indicatedthat we prepared the assembly of exposed crystal surface-controlled rutile TiO2nanorodmicrospheres with the diameters of approximately3.5μm to2μm. The XRD and ramanspectra results indicated that the phase of product prepared without NaCl had thepresence of rutile and brookite mixed-phase TiO2, but addition of NaCl to the solutionresults that correspond to TiO2in rutile form, no other phases are found. These resultsindicated that NaCl favored the formation of rutile TiO2. At the same time, increasingthe NaCl concentration was known to promote smaller grain sizes. The SEM indicatedthat rice-like TiO2nanorods that were of20–30nm in diameter and100–200nm inlength formed in the absence of NaCl. Addition of NaCl to the synthesis system resultedin the formation of TiO2assembled nanorod microspheres, which TiO2microsphereswere composed of densely packed rice-like TiO2nanorods arranged along the long axisof the nanorods parallel to the center of the microsphere. As the NaCl concentration inaqueous solution increased, the diameter of the microspheres decreased. TEM andHRTEM images further confirmed that TiO2nanorods were the building blocks of thesemicrospheres. The sample prepared without NaCl showed nanorod structures with neattips. After hydrothermal treatment with NaCl, the shape of the nanorod ends changedfrom a symmetric triangular tip to a symmetric large square tip as the NaClconcentration was increased from1.0mol L–1to2.0mol L–1. The area of the exposed(111) crystal faces gradually decreased with the increase in NaCl concentration. At the same time, a new face, the (001) face, was generated and gradually became increasinglyexposed.The photocatalytic degradation of papermaking wastewater were investigatedusing our synthesized samples. The effects of various parameters such as catalystdosage, solution pH, and irradiation time on the photocatalytic activity of the fabricatedTiO2powders were discussed. At the optimum dose of1.0g L1TiO2at pH4.0, thesamples exhibited the highest photocatalytic activity. The photocatalytic activity ofsamples after three cycles kept better, these results further confirmed that samples hadbetter stability and can be reused. Rutile TiO2nanorod-based microspheres (S-7)showed the highest photocatalytic activity among the prepared TiO2samples, the CODCrand chroma removal rates of S-7were approximately68.2%and100%, respectively,after12h of photodegradation, which exposed well-developed (001) faces mayfacilitate the separation of electrons and holes, resulting in photocatalytic activityenhancement. Therefore, the activities of the samples for the photocatalytic degradationof wastewater were affected by the newly exposed crystal surface (001) of rutile TiO2.