Colorless Organic Pollutants Research Articles

Facile synthesis of Pd nanoparticles dispersed polypyrrole-carbon black/NiO nanocomposite with enhanced photocatalytic degradation of colored and colorless organic pollutants

Creation and designing of efficient visible-light responsive photocatalysts requires highly precise and extremely determined efforts in order to obtain material with promising properties and efficient transfer of charge carriers. In this work, we aim to develop and manufacture a distinct visible light photocatalyst consisting of NiO nanostructures, polypyrrole doped carbon black (PPyC) and Pd nanoparticles for wastewater treatment. The Pd NPs and PPyC doped NiO trio photocatalyst was developed via simple ultrasonication and photoreduction methods. XRD analysis showed that NiO has crystalline face centered cubic structure while the successful development of ternary photocatalyst was smoothly confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) studies. Transmission electron microscopy (TEM) images showed that NiO possessed fine irregular shape particles with size ranging from 20 to 50 nm grown abundantly in huge density, while the PPyC exhibited beads shape structures interconnected with each other giving chain like appearance. The diffuse reflectance UV–vis spectra showed red shift and lowering in bandgap upon Pd and PPyC doping. The newly produced Pd-PPyC@NiO photocatalyst has been exploited for the photocatalytic removal of colorless insecticide imidacloprid and colored methylene blue (MB) dye under visible light irradiation. The newly created Pd-PPyC@NiO photocatalyst removed 96.0% of imidacloprid just in 20 min representing ⁓ 3 times more efficient than bare NiO. Furthermore, Pd-PPyC@NiO photocatalyst was exceptionally well towards the destruction of MB under same visible light source, indicating its potential use in photocatalysis.

Novel CdS/CeO2/g-C3N4 nanocomposite for efficient phenol photodegradation under visible light

Higher electron transfer efficiency is an important way to improve the activity of photocatalysts. A novel Z-scheme CdS/CeO2/g-C3N4 nanocomposite was successfully synthesized by a solvothermal method, and its photocatalytic activity was evaluated by the degradation of phenol. The phase structure, morphology, surface structure, and atomic valence state of the as-obtained photocatalyst were characterized by XRD, SEM, TEM, FT-IR, XPS, and UV–Vis absorption spectroscopy, respectively. The CdS/CeO2/g-C3N4 nanocomposite exhibited a remarkable photocatalytic activity and a rapid degradation ability for phenol with a degradation rate of 95 % in 180 min, which was considerably better than those of pure CeO2 and CdS/CeO2 under the same conditions, suggesting a synergistic effect in the nanocomposite. The enhancement of the photocatalysis ability of the nanocomposite is mainly attributed to the higher adsorption capacity of three-dimensional porous g-C3N4 and the three-dimensional space electric field formed by its complex with CdS and CeO2. The three-dimensional porous structure is not only conducive to the efficient adsorption of pollutants but also provides active sites for photocatalytic reactions. The three-dimensional space and the network interconnection structure are conducive to the directional migration of photogenerated charges and increase the carrier lifetime. In brief, this work provides a new route to the design and synthesis of CdS/CeO2/g-C3N4 for colorless organic pollutants photodegradation under visible light.

PH-induced structural evolution, photodegradation mechanism and application of bismuth molybdate photocatalyst

In this work, we have elucidated the pH-induced structural evolution of bismuth molybdate photocatalyst based on a hydrothermal synthesis route. With increasing the pH value of precursor solution, pure Bi2MoO6 was synthesized at pH 2–5, Bi2MoO6-Bi4MoO9 mixture was obtained at pH 7–9, pure Bi4MoO9 was obtained at pH 11, and pure α-Bi2O3 was derived at pH 13. The as-derived samples mainly present particle-like shapes but with different particle sizes (except the observation of Bi2MoO6 nanowires in sample S-pH9). The photocatalytic performances between the samples were compared via the degradation of methylene blue (MB) under irradiation of simulated sunlight. The Bi2MoO6 sample synthesized at pH 2 exhibited the highest photodegradation performance (η(30 min) = 89.8 %, kapp = 0.05007 min−1) among the samples. The underlying photocatalytic mechanism and degradation pathways of MB were systematically analyzed. Moreover, the photodegradation performance of the Bi2MoO6 photocatalyst was further evaluated at different acidic-alkaline environments as well as in degrading various color and colorless organic pollutants, which provides an important insight into its practical application.

Simple Low Temperature Technique to Synthesize Sillenite Bismuth Ferrite with Promising Photocatalytic Performance

Sillenite-type members of the bismuth ferrite family have demonstrated outstanding potential as novel photocatalysts in environmental remediation such as organic pollutant degradation. This investigation has developed a low temperature one-step hydrothermal technique to fabricate sillenite bismuth ferrite Bi25FeO40 (S-BFO) via co-substitution of 10% Gd and 10% Cr in Bi and Fe sites of BiFeO3, respectively, by tuning hydrothermal reaction temperatures. Rietveld refined X-ray diffraction patterns of the as-synthesized powder materials revealed the formation of S-BFO at a reaction temperature of 120–160 °C. A further increase in the reaction temperature destroyed the desired sillenite structure. With the increase in the reaction temperature from 120 to 160 °C, the morphology of S-BFO gradually changed from irregular shape to spherical powder nanomaterials. The high-resolution TEM imaging demonstrated the polycrystalline nature of the S-BFO(160) nanopowders synthesized at 160 °C. The as-synthesized samples exhibited considerably high absorbance in the visible region of the solar spectrum, with the lowest band gap of 1.76 eV for the sample S-BFO(160). Interestingly, S-BFO(160) exhibited the highest photocatalytic performance under solar irradiation, toward the degradation of rhodamine B and methylene blue dyes owing to homogeneous phase distribution, regular powder-like morphology, lowest band gap, and quenching of electron–hole pair recombination. The photodegradation of a colorless organic pollutant (ciprofloxacin) was also examined to ensure that the degradation is photocatalytic and not dye-sensitized. In summary, Gd and Cr co-doping have proven to be a compelling energy-saving and low-cost approach for the formulation of sillenite-phase bismuth ferrite with promising photocatalytic activity.

Facile synthesis of NiO/ZnO nano-composite by Co-precipitation, characterization and photocatalytic study of colored and colorless organic pollutants by solar irradiation

A facile strategy of co-precipitation and ultra-sonication was used for the formation of pristine metal oxides (NiO and ZnO) and NiO/ZnO nanocomposite respectively. X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) were used for the structural, spectral and morphological analysis of as synthesized sample. The band gap value of NiO/ZnO nanocomposite was 1.87eV. The crystalline size of the nano-composite calculated using XRD data is 10.88 nm. Photocatalytic ability of as synthesized samples was examined for the degradation of methylene blue, Rhodamine-B and Benzoic acid. The percentage degradation of methylene blue using NiO, ZnO and NiO/ZnO nanocomposite was 54%, 81.5% and 97.1% while in case of Rhodamine-B and Benzoic acid the degradation efficiency of as synthesized samples was 49.6%, 77% and 88.1% for Rhodamine B and 59.2%, 81.3 and 93.2 for Benzoic acid. This enhanced photocatalytic ability of nanocomposite make it a potential candidate for removal of organic pollutants from waste water.

Facile Synthesis of Nio/Zno Nano-Composite by Co-Precipitation, Characterization and Photocatalytic Study of Colored and Colorless Organic Pollutants by Solar Irradiation

Facile Synthesis of Nio/Zno Nano-Composite by Co-Precipitation, Characterization and Photocatalytic Study of Colored and Colorless Organic Pollutants by Solar Irradiation

ZnTi layered double hydroxides as photocatalysts for salicylic acid degradation under visible light irradiation

A series of ZnTi layered double hydroxides (LDH) with different Zn/Ti ratios are prepared and used as catalysts for photodegradation of salicylic acid (SA) under visible light. The catalysts are characterized by X-Ray diffraction, diffuse reflectance infrared Fourier transform spectroscopy, UV–vis diffuse reflectance spectroscopy, thermogravimetry, electron paramagnetic resonance and N2 adsorption-desorption. The results show that SA anions bind to the LDH surface and that an electron can be excited from the HOMO in the adsorbed molecules to the conduction band of the LDH under visible light illumination. This charge transfer further leads to an effective photodegradation and mineralization of SA with better conversion results than on P25 titania. Key factors influencing the charge-transfer process in LDH are the high surface area and the Ti/Zn ratio of the LDH materials. The combination of highly dispersed Zn2+ and Ti4+ cations in the brucite-like sheets of the LDH allows for a better charge separation, which also accounts for the high photocatalytic activity. The present results show that superoxide radicals play a role in the visible-light induced degradation of SA on LDH, while no •OH radicals are formed. In contrast to LDH, the light-induced degradation pathway of SA over P25 titania leads to the formation of CO2−, a relatively stable anion that may hamper further conversion to CO2 and hence limit the photocatalytic performance. The introduction of an electron acceptor, such as peroxydisulfate, further improves the degradation and mineralization of SA over LDH, but care should be taken not to use an electron acceptor that can easily adsorb to the LDH surface, such as H2O2. ZnTi LDH are thus very promising alternatives to TiO2 for the photodegradation of colorless organic pollutants, such as SA, under visible light irradiation.

The Effect of Molar Ratios of Ti/Si on Core-Shell SiO2@TiO2 Nanoparticles for Photocatalytic Applications

After the core-shell SiO2@TiO2 nanoparticles (CSTNs) were synthesized by hydrothermal method, we investigated the influence of different molar ratios of Ti/Si on morphology, structure, and photocatalytic activity of the CSTNs. It was found that the CSTNs showed different size and surface morphology as the Ti/Si molar ratio changed. Besides, the TiO2 and the CSTN had the anatase phase after hydrothermal process and calcination at 450°C for 2 h. The N2 adsorption-desorption isotherms demonstrated the CSTNs with the molar ratio of Ti/Si increased from 1 : 1 to 8 : 1 can be categorized as type IV with hysteresis loop of type H2 and showed to be mesoporous materials. In addition, the CSTNs with the Ti/Si molar ratio of 5 : 1 had the highest surface area of 176.79 m2/g. Surface charges showed the isoelectric point (IEP) of the CSTNs ranged between silica (IEP at pH 3.10) and titania (IEP at pH 5.29). Since the molar ratio of Ti/Si increased from 1 : 1 to 8 : 1 by degradating both colorless organic pollutant of phenol and colored substances of methylene blue (MB) under UV irradiation, the photocatalytic activity of CSTNs exhibited higher photodegradation efficiency compared with TiO2. What is more, the experimental results also showed the CSTNs with Ti/Si molar ratio of 5 : 1 had the highest photocatalytic activity and showed higher photocatalytic efficiency compared with other TiO2-SiO2 composites reported for photodegradation of phenol and MB.

Fabrication of oxygen-vacancy-rich black-BiOBr/BiOBr heterojunction with enhanced photocatalytic activity

Photocatalysis, as an advanced oxidization process, has been extensively studied in environmental remediation. To suppress the recombination of photogenerated charge carriers, a novel oxygen-vacancy-rich black BiOBr/BiOBr isotype heterojunction has been successfully fabricated by surface hydrogenation. As-prepared samples were comprehensively characterized by various techniques. Photocatalytic activity of as-prepared samples was measured via degradation of colorless organic pollutant (phenol) in water under visible light. It was found that over 90% of phenol were removed over 210 min under visible light, which was double and 4.5 times higher than that of black BiOBr and pure BiOBr, respectively. The enhancement in photocatalytic activity may be attributed to the synergistic effects of isotype heterojunction and oxygen vacancy. Formation of heterojunction facilitated photogenerated charge carriers’ separation. And the surface oxygen vacancies acted electrons acceptors and reactive sites in photocatalytic oxidization process. This work sheds a light on the significance of oxygen vacancies in improving photocatalytic activity.

One-pot low-temperature synthesis of BiOX/TiO2 hierarchical composites of adsorption coupled with photocatalysis for quick degradation of colored and colorless organic pollutants

BiOX/TiO2 (X = Cl, Br, and I) hierarchical composites with superior photoelectrochemical performances were successfully synthesized by one-pot low-temperature solvothermal process without any structure-directing agents. The dual functions of adsorption coupled with photocatalysis based on BiOX/TiO2 were fully exhibited in terms of the quick degradation of colored and colorless organic pollutants (OPs). The as-prepared composites were characterized by field-emitting scanning electron microscope (FESEM), X-ray power diffraction (XRD) analysis, transmission electron microscope (TEM), N2 adsorption/desorption, UV–vis diffuse reflectance spectra (DRS), photoluminescence spectra (PL), photocurrent measurements (PC), and electrochemical impedance spectroscopy (EIS), respectively. As-prepared BiOX/TiO2 composites exhibited outstanding photoelectrochemical activities. Especially, the considerably enhanced adsorption and photocatalytic efficiencies were observed in the optimized BiOCl/TiO2 composites compared to their counterparts. The improvement of adsorption and photocatalytic performances should be ascribed to the presence of columbite TiO2-II in anatase, which would not only improve the ability of absorbing visible light and the charge separation efficiency, but also to effectively tailor the particle size, surface area and the exposed active facet of composites.

Interactive Fe2O3/porous SiO2 nanospheres for photocatalytic degradation of organic pollutants: Kinetic and mechanistic approach

A uniformly distributed mesoporous silica nanospheres has been successfully synthesized. Silica nanospheres have been loaded with different content of Fe2O3 nanoparticles synthesized by the sol-gel process followed by calcination to form the Fe2O3 supported on silica nanospheres composite. The as-synthesized photocatalyst has been characterized for crystal structure, morphology, stability, surface area and also surface composition was determined. The photocatalytic oxidation ability of the composite photocatalyst was evaluated by degrading aqueous solutions of Methylene Blue and Congo red dyes under visible light having intense absorption in the wavelength range between 550 and 560 nm. The prime significance of silica is to act as catalyst support for uniform distribution of hematite particles for enhanced catalytic reactivity. Highest degradation has been achieved with 20 wt % loading of hematite nanoparticles indicating the less agglomeration and availability of more catalytic sites. Furthermore, colorless organic pollutants 2-chlorophenol and 2, 4-dichlorophenol have been degraded with high efficiency in the presence of H2O2 oxidizer. The scavenger experiments confirmed that hydroxyl radicals are the majorly participating species in this catalytic system. The composite system also shows good recyclability of the materials and advocates the promising nature of the designed system for multiple hazardous environmental contaminants.

CdZnS solid solution supported Ce2Sn2O7 pyrochlore photocatalyst that proves to be an efficient candidate towards the removal of organic pollutants

Novel Ce2Sn2O7/CdZnS nanostructure has been constructed successfully by the hydrothermal methods. The CdZnS solid solution act as an excellent supporting material to the pyrochlore Ce2Sn2O7 nanorods. Several characterization techniques have been applied to explore the phase structure, elemental composition, optical properties and photoinduced catalytic activity. The photocatalytic activity of the Ce2Sn2O7 rod/ CdZnS solid solution and pure Ce2Sn2O7, CdZnS and CdS materials were investigated under visible light and direct solar irradiation with ambient environment. The obtained Ce2Sn2O7/CdZnS nano composite possess increased photocatalytic activity for the degradation of Rh B as well as various organic pollutants. Moreover, the Ce2Sn2O7/CdZnS shows the good photocatalytic efficiency for the colorless organic pollutants. The increased photocatalytic activity of the Ce2Sn2O7/CdZnS is due to the close contact between the Ce2Sn2O7 and CdZnS nanomaterials. To confirm the role of the reactive species in the photocatalytic reaction, the trapping experiments have been conducted and the results are discussed with the detailed information.

Fabrication of a magnetically separable and dual Z-scheme PANI/Ag3PO4/NiFe2O4 composite with enhanced visible-light photocatalytic activity for organic pollutant elimination

A novel polyaniline/silver phosphate/nickel ferrate (PANI/Ag3PO4/NiFe2O4) magnetic photocatalyst has been successfully fabricated by a precipitation-hydrothermal method. The composition, morphological structure and optical property of the as-prepared samples are characterized. All the PANI/Ag3PO4/NiFe2O4 composites with different PANI content show enhanced visible-light photocatalytic activity for rhodamine B (RhB) and methyl orange (MO) dyes degradation compared to pure Ag3PO4, Ag3PO4/NiFe2O4 and Ag3PO4/PANI composites. The highest degradation efficiency for RhB and MO via 3%-PANI/Ag3PO4/NiFe2O4 composite photocatalyst separately reach 100% and 94.97%, and their degradation rate (k) are close to 12.1 and 15.4 times faster than those of pure Ag3PO4, respectively. Meanwhile, the PANI/Ag3PO4/NiFe2O4 composite displays excellent photocatalytic performance on the degradation of colorless organic pollutants (tetracycline hydrochloride, nitrobenzene and bisphenol A) under the visible light irradiation. The PANI/Ag3PO4/NiFe2O4 catalyst exhibits a superior stability than pure Ag3PO4 after three consecutive reuses. The improved photocatalytic activity and stability of PANI/Ag3PO4/NiFe2O4 ternary composite can be attributed to the extended absorption capability in the visible light region as well as the high-efficiency separation of electron-hole pairs. Particularly, the construction of double Z-scheme heterojunctions in the ternary composite can facilitate the rapid transfer of electrons on the surface of Ag3PO4, thus inhibit its photocorrosion. This study provides an idea for enhancing the anti-photocorrosion and photocatalytic activity of photosensitive semiconductors.

Defective black Ti3+ self-doped TiO2 and reduced graphene oxide composite nanoparticles for boosting visible-light driven photocatalytic and photoelectrochemical activity

We present a facile and environmentally friendly way to successfully build partially reduced titanium dioxide nanoparticles integrated with reduced graphene oxide composite nanosheets (RGO/TiO2−x) through an environmental solvothermal method at relatively low temperature. The Ti3+ self-doping of TiO2−x is conducive to enhance its visible light absorption, and the existence of RGO as the electron receiver makes the electrons on TiO2−x transport better to its surface, effectively promoting the separation of electrons and holes. Experiments on photocatalytic degradation of methylene blue dye and phenol colorless organic pollutant by visible light demonstrate that the RGO/TiO2−x assemblies exhibit the highest photocatalytic activity, and that methylene blue solution concentration of used in the experiment is 40 mg L−1, which was more higher than the concentration (10 mg L−1) used in many of reported articles. Compared to the pure TiO2 and TiO2−x, the photodegradation efficiency of methylene blue and phenol can be increased to 100% within 120 min and 150 min under visible light. Moreover, the mineralization rates of MB, such as the total organic carbon (TOC) degradation rate, can reach to 75.7%, 86.6% and 89.4% for m-RGO/TiO2−x, respectively. And the reaction efficiency of RGO/TiO2−x is basically not much changed after 4th cycles, suggesting its excellent photocatalytic stability.

Reduced graphene oxide-modified Bi2WO6/BiOI composite for the effective photocatalytic removal of organic pollutants and molecular modeling of adsorption

In this study, reduced graphene oxide (rGO) with unique physicochemical, optical, and electrical properties was applied in a varying content to improve the photocatalytic performance of Bi2WO6/BiOI towards the degradation of colorless organic pollutants: acetaldehyde (AcH) and chloramphenicol (CAP) under visible light. The rGO/Bi2WO6/BiOI composites were characterized by means of X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, X-ray photoelectron spectroscopy, and nitrogen gas adsorption analysis. The prepared rGO/Bi2WO6/BiOI composite with 1 wt% rGO demonstrated a much higher photodegradation rate constant towards the degradation of AcH and CAP than its Bi2WO6/BiOI counterpart. Such enhancement can be explained by the synergistic effects of rGO in adsorbing AcH and CAP molecules, capturing photoinduced electrons, and forming an additional p-n heterojunction with n-type Bi2WO6. The adsorption affinities of AcH molecules in the gas phase and CAP molecules in aqueous solution to model rGO, BiOI (102) and Bi2WO6 (113) surfaces were studied by molecular modeling using a layer building tool that allows the generation of layered structures and interfaces. It was found that compared to Bi2WO6, rGO and BiOI show the increased adsorption of AcH and CAP+water molecules over the rGO/BiOI surface in the rGO/Bi2WO6/BiOI and rGO/BiOI composites. The enhanced photocatalytic activity demonstrated by the newly prepared rGO/Bi2WO6/BiOI composite makes it a potential candidate for use in environmental remediation processes.

An advanced TiO2/Fe2TiO5/Fe2O3 triple-heterojunction with enhanced and stable visible-light-driven fenton reaction for the removal of organic pollutants

The construction of catalysts with high efficiency and stability for heterogeneous Photo-Fenton reaction Heterogeneous (PFR) has been a major challenge for the degradation of organic pollutants. Here, we successfully develop an advanced TiO2/Fe2TiO5/Fe2O3 triple-heterojunction structure by using the mesoporous TiO2 spheres as the substrate via a simple ion-exchange method. The XRD and HRTEM results demonstrate the generation of Fe2TiO5 on the interface between TiO2 and Fe2O3, which can be used as a “bridge” to transfer the photo-excited electrons from TiO2 to Fe2O3. The as-prepared triple-heterojunction has abundant interphase boundaries which greatly improve the migration of photo-excited charges among different components. As a result, the prepared triple-heterojunction has a significantly enhanced PFR activity for the visible-light-driven degradation of methyl orange (MO) and colorless organic pollutant of phenol, compared with the single catalysts of Fe2O3 and TiO2, and the binary-heterojunction of TiO2/Fe2O3. Compared to the traditional Fe2O3 based PFR, the degradation rates of MO and phenol over triple-heterojunction can be increased from 4% to 87% within 10min irradiation and from 38% to 100% within 60min irradiation, respectively. And the total organic carbon (TOC) degradation rate of phenol can be up to 85%. Moreover, this advanced triple-heterojunction has a wide pH value range of application in PFR. Either at a pH of 4.0 or 7.0, it shows a much higher and more stable PFR activity for the degradation of MO than the catalysts of Fe2O3 and TiO2/Fe2O3. And the reaction rate of TiO2/Fe2TiO5/Fe2O3 almost keeps changeless even after 10th cycles, suggesting its vast application foreground in the environmental pollutant treatment.

Self-Sensitized Photocatalytic Degradation of Colorless Organic Pollutants Attached to Rutile Nanorods—Experimental and Theoretical DFT+D Studies

Utilization of visible light by photosensitization of semiconductor photocatalysts via surface attachment of small colorless organic pollutants (COP) is an effective way to stimulate their photocatalytic degradation. Herein, by means of the spectroscopic, photoelectrochemical, spectroelectrochemical, and photocatalytic studies combined with the DFT+D molecular modeling, we show how disubstituted benzene derivatives, like catechol (CAT), salicylic acid (SAL), phthalic acid (PTA), and terephthalic acid (TPA), can tune the photocatalytic properties of rutile nanorods with the dominant (110) termination. We elucidated in a systematic way the COP ligand-binding configurations, the alignment of energy levels, and the charge-transfer pathways from the organic admolecules to the titania substrate. The pDOS structures of the COP@r-TiO2(110) assemblies were interpreted in terms of electronic interactions between the titania photocatalyst and the COP adspecies. It was shown that the appearance of additional states w...

Reduced graphene oxide-silver nanoparticle composite as visible light photocatalyst for degradation of colorless endocrine disruptors.

Sunlight-induced degradation of organic pollutants is an ideal approach for environmental pollution control and wastewater treatment. Although a variety of photocatalysts have been designed toward this goal, efficient degradation of colorless organic pollutants by visible light is a challenging issue. Here, we show that a reduced graphene oxide (rGO)-based composite with silver nanoparticle (rGO-Ag) can act as an efficient visible-light photocatalyst for the degradation of colorless organic pollutants. We have developed a simple, large-scale synthesis method for rGO-Ag and used it for the degradation of three well-known endocrine disruptors (phenol, bisphenol A, and atrazine) under UV and visible light. It is found that photocatalytic efficiency by rGO-Ag under visible light is significantly higher compared to that of rGO or silver nanoparticles. It is proposed that Ag nanoparticles offer visible-light-induced excitation of silver plasmons, and conductive rGO offers efficient charge separation and thus induces oxidative degradation of the organic pollutant. This approach can be extended for sunlight-induced degradation of different organic pollutants.

Yellow–colored mesoporous pure titania and its high stability in visible light photocatalysis

Abstract Yellow–colored pure titania with a mesoporous structure was prepared by the aggregate of titania nanocrystals, which were stabilized by exfoliated titanate nanosheets via an electrostatic interaction. X–ray diffraction patterns and images of transmission electron microscope confirm that titanate sheets are randomly dispersed into the assembled titania nanocrystals without forming any self–restacked phase. This nanocrystals–nanosheets composite exhibits a mesoporous structure with pore size of ~ 6.5 nm and surface area of 236.3 m 2 g − 1 . Greatly different from the UV–responded properties of titania nanocrystals and titanate nanosheets, the absorption edge of nanocomposite red–shifts to visible light region. The visible light photocatalytic tests demonstrate that this nanocomposited titania shows excellent activity for the degradation of organic dyes, as well as a colorless organic pollutant of 2, 4–dichlorophenol. The possible photocatalytic mechanism that photogenerated holes as the mainly oxidant species in photocatalysis is proposed based on the trapping experiments of hydroxyl radicals or photogenerated holes. Moreover, as the nanocomposite depicts an extreme stability, no obvious deactivation occurs after five cycles.

Synthesis of Efficient Nanosized Rutile TiO2 and Its Main Factors Determining Its Photodegradation Activity: Roles of Residual Chloride and Adsorbed Oxygen

Nanosized TiO2 containing different contents of rutile phase was controllably synthesized by a hydrochloric acid-modified hydrothermal process. It is demonstrated that the formation of rutile phase in TiO2 mainly depends on the role of chlorine anions in the synthesis, and a certain amount of residual chloride would exist on the surfaces of the resulting nanocrystalline rutile TiO2. Interestingly, the as-prepared rutile shows high activity for photodegradation of rhodamine B dye compared with the as-prepared anatase, even superior to the P25 TiO2. It is mainly attributed to the residual chloride that could promote the dye adsorbed on the surfaces of TiO2, consequently accelerating the photosensitization oxidation reactions of the dye molecules. In the photodegradation of liquid-phase phenol and gas-phase aldehyde, the as-prepared rutile TiO2 samples display low activity, which is attributed to the photogenerated electrons weakly captured by the adsorbed oxygen, since the residual chloride could effectively capture photoinduced holes based on the atmosphere-controlled surface photovoltage spectroscopy results. Further, the photoactivity of resulting rutile for degrading phenol and aldehyde is greatly enhanced by modifying a proper amount of phosphoric acids to increase the adsorption of O2, even higher than that of the P25 TiO2. This work would explore feasible routes to synthesize efficient nanosized rutile TiO2-based photocatalysts for degrading colored and colorless organic pollutants by investigating the rate-determining factors in the photodegradation processes.