Surface modification of inorganic nanoparticles for development of organic–inorganic nanocomposites—A review

Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO 2 . There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.

A review of ZnO nanoparticles as solar photocatalysts: Synthesis, mechanisms and applications

An overview on limitations of TiO2-based particles for photocatalytic degradation of organic pollutants and the corresponding countermeasures

This paper reviews recent studies on the semiconductor photocatalysis based on surface-modified TiO2 of which application is mainly focused on environmental remediation. TiO2 photocatalysis that is based on the photoinduced interfacial charge transfer has been extensively studied over the past four decades. A great number of modification methods of semiconductor photocatalysts have been developed and investigated to accelerate the photoconversion, to enable the absorption of visible light, or to alter the reaction mechanism to control the products and intermediates. In this regard, various modification methods of TiO2 are classified according to the kind of surface modifiers (metal-loading, impurity doping, inorganic adsorbates, polymer coating, dye-sensitization, charge transfer complexation) and their effects on photocatalytic reaction mechanism and kinetics are discussed in detail. Modifying TiO2 in various ways not only changes the mechanism and kinetics under UV irradiation but also introduces visible light activity that is absent with pure TiO2. Each modification method influences the photocatalytic activity and mechanism in a way different from others and the observed modification effects are often different depending on the test substrates and conditions even for the same modification method. Better understanding of the modification effects on TiO2 photocatalysis is necessary to obtain reliable results, to assess the photoconversion efficiency more quantitatively, and to further improve the modification methods.

Surface modification of TiO2 photocatalyst for environmental applications

Visible light-responsive photocatalytic technology holds great potential in water treatment to enhance purification efficiency, as well as to augment water supply through the safe usage of unconventional water sources. This review summarizes the recent progress in the design and fabrication of visible light-responsive photocatalysts via various synthetic strategies, including the modification of traditional photocatalysts by doping, dye sensitization, or by forming a heterostructure, coupled with π-conjugated architecture, as well as the great efforts made within the exploration of novel visible light-responsive photocatalysts. Background information on the fundamentals of heterogeneous photocatalysis, the pathways of visible light-responsive photocatalysis, and the unique features of visible light-responsive photocatalysts are presented. The photocatalytic properties of the resulting visible light-responsive photocatalysts are also covered in relation to the water treatment, i.e., regarding the photocatalytic degradation of organic compounds and inorganic pollutants, as well as photocatalytic disinfection. Finally, this review concludes with a summary and perspectives on the current challenges faced and new directions in this emerging area of research.

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Recent developments in heterogeneous photocatalytic water treatment using visible light-responsive photocatalysts: a review

Titanium dioxide nanoparticles were modified by polyaniline (PANI) using ‘in situ’ chemical oxidative polymerization method in hydrochloric acid solutions. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectrum (XPS) and UV–vis spectra were carried out to characterize the composites with different PANI contents. The photocatalytic degradation of phenol was chosen as a model reaction to evaluate the photocatalytic activities of the modified catalysts. Results show that TiO2 nanoparticles are deposited by PANI to mitigate TiO2 particles agglomeration. The modification does not alter the crystalline structure of the TiO2 nanoparticles according to the X-ray diffraction patterns. UV–vis spectra reveal that PANI-modified TiO2 composites show stronger absorption than neat TiO2 under the whole range of visible light. The resulting PANI-modified TiO2 composites exhibit significantly higher photocatalytic activity than that of neat TiO2 on degradation of phenol aqueous solution under visible light irradiation (λ ≥ 400 nm). An optimum of the synergetic effect is found for an initial molar ratio of aniline to TiO2 equal to 1/100.

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Sunlight photocatalytic activity of polypyrrole–TiO2 nanocomposites prepared by ‘in situ’ method

A series of polypyrrole (PPy)/titanium dioxide (TiO2) nanocomposites were prepared in different polymerization conditions by ‘in situ’ chemical oxidative polymerization. The nanocomposites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy spectra (XPS), and UV–Vis diffuse reflectance spectra. The photocatalytic degradation of methyl orange (MO) was chosen as a model reaction to evaluate the photocatalytic activities of TiO2/PPy catalysts. The results show that a strong interaction exists at the interface between TiO2 and PPy, the deposition of PPy on TiO2 nanoparticles can alleviate their agglomeration, PPy/TiO2 nanocomposites show stronger absorbance than neat TiO2 under the whole range of visible light. The obtained PPy/TiO2 nanocomposites exhibit significantly higher photocatalytic activity than the neat TiO2 on the degradation of MO aqueous solution under visible and UV light illumination. The reasons for improving the photocatalytic activity were also discussed.

Photocatalytic activity of polypyrrole/TiO2 nanocomposites under visible and UV light

BACKGROUND: Nanoparticulate titanium dioxide (TiO2) has the advantages of high chemical stability, high photocatalytic activity to oxidise pollutants in air and water, relatively low price and non-toxicity. However, its high surface energy leads to the aggregation of nanoparticles. In addition, the wide band gap of TiO2 (3.2 eV) only allows it to absorb ultraviolet (UV) light (<387 nm), which represents just a small fraction (3–5%) of the solar photons. These factors have limited its use in many fields. In this study, nanoparticulate TiO2 was modified by polyaniline (PANI) in order to enhance its photoactivity under UV light and sunlight illumination.



RESULTS: TiO2 nanoparticles were modified by PANI via a chemical oxidative method. The introduction of small amounts of PANI enhanced the dispersion of TiO2 nanoparticles and improved the photocatalytic activity under UV light. In addition, the band gap energies of all PANI/TiO2 nanocomposites were lower than that of neat TiO2 nanoparticles, so the PANI/TiO2 nanocomposites can be excited to produce more electron–hole pairs under sunlight, which could result in higher photocatalytic activities.



CONCLUSION: The modification of nanoparticulate TiO2 by PANI can increase its photoactivity in the process of phenol degradation under UV light and sunlight illumination. Copyright © 2008 Society of Chemical Industry

Yanhong Wang

Papers

Preparation of polyaniline-modified TiO2 nanoparticles and their photocatalytic activity under visible light illumination

Sunlight photocatalytic activity of polypyrrole–TiO2 nanocomposites prepared by ‘in situ’ method

Photocatalytic activity of polypyrrole/TiO2 nanocomposites under visible and UV light

Surface modification of titanium dioxide nanoparticles by polyaniline via an in situ method

Controlled synthesis of NiCoP@NiM LDH (M=Cu, Fe, Co) as efficient hydrogen evolution reaction electrocatalyst