Abstract
A series of high activity photocatalysts g-C3N4-TiO2 were synthesized by simple one-pot thermal transformation method and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller (BET) surface area, and ultraviolet–visible diffuse reflectance spectroscopy (UV-Vis-DRS). The g-C3N4-TiO2 samples show highly improved photoreductive capability for the degradation of polybromodiphenyl ethers compared with g-C3N4 under visible light irradiation. Among all the hybrids, 0.02-C3N4-TiO2 with 2 wt % g-C3N4 loaded shows the highest reaction rate, which is 15 times as high as that in bare g-C3N4. The well-matched band gaps in heterojunction g-C3N4-TiO2 not only strengthen the absorption intensity, but also show more effective charge carrier separation, which results in the highly enhanced photoreductive performance under visible light irradiation. The trapping experiments show that holetrapping agents largely affect the reaction rate. The rate of electron accumulation in the conductive band is the rate-determining step in the degradation reaction. A possible photoreductive mechanism has been proposed.
Highlights
Persistent organic pollutants (POPs) are of significant concern because they are bioaccumulative and harmful to human health [1,2,3,4]
The transmission electron microscopy (TEM) image displays the inner structure of the catalyst
The TEM image of g-C3 N4 -TiO2 shows that TiO2 particles disperse on the surface of g-C3 N4 with sizes 5–10 nm (Figure 1b)
Summary
Persistent organic pollutants (POPs) are of significant concern because they are bioaccumulative and harmful to human health [1,2,3,4]. TiO2 has attracted much attention in this field for the degradation of POPs due to its excellent photocatalytic capability, high chemical stability, and environmental friendliness [6]. Carbon nitride (C3 N4 ) with graphite-like structure—being a wide-band-gap semiconductor—has received wide attention in catalytic applications due to its high chemical stability and appealing electronic structure [8]. The optical band gap of g-C3 N4 is 2.7 eV (ECB = −1.3 V, EVB = 1.4 V vs NHE, pH = 7; CB: conduction band, VB: valence band, NHE: normal hydrogen electrode), which gives it promising performance in photocatalytic activity [9]. G-C3 N4 was able to split water into hydrogen or oxygen in the presence of an electron donor or acceptor under irradiation [10]. H2 O2 could be activated by g-C3 N4 for the oxidation of benzene to phenol [11]
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