Synthesis and Characterization of Novel Plasmonic Ag/AgX-CNTs (X = Cl, Br, I) Nanocomposite Photocatalysts and Synergetic Degradation of Organic Pollutant under Visible Light

Abstract

A series of novel well-defined Ag/AgX (X = Cl, Br, I) loaded carbon nanotubes (CNTs) composite photocatalysts (Ag/AgX-CNTs) were fabricated for the first time via a facile ultrasonic assistant deposition−precipitation method at the room temperature (25 ± 1°C). X-ray diffraction, X-ray photoelectron spectroscopy, nitrogen adsorption−desorption analysis, scanning electron microscopy, and ultraviolet−visible light absorption spectra analysis were used to characterize the structure, morphology, and optical properties of the asprepared photocatalysts. Results confirmed the existence of the direct interfacial contact between Ag/AgX nanoparticles and CNTs, and Ag/AgX-CNTs nanocomposites exhibit superior absorbance in the visible light (VL) region owing to the surface plasmon resonance (SPR) of Ag nanoparticles. The fabricated composite photocatalysts were employed to remove 2,4,6-tribromophenol (TBP) in aqueous phase. A remarkably enhanced VL photocatalytic degradation efficiency of Ag/AgX-CNTs nanocomposites was observed when compared to that of pure AgX or CNTs. The photocatalytic activity enhancement of Ag/AgX-CNTs was due to the effective electron transfer from photoexcited AgX and plasmon-excited Ag(0) nanoparticles to CNTs. This can effectively decrease the recombination of electron−hole pairs, lead to a prolonged lifetime of the photoholes that promotes the degradation efficiency. KEYWORDS: plasmonic photocatalyst, carbon nanotube supporter, silver halides, visible light, photocatalytic activity ■ INTRODUCTIONPhotocatalysis technique, as a cost-effective means for solar energy utilization, hydrogen production, and environmental purification, has been focused by many researchers. 1−7 In recent years, highly efficient visible-light-driven (VLD) photocatalyst development has been recognized as an important goal in the field of photocatalysis. Generally, two major approaches have been frequently employed to fabricate VLD photocatalyst. One is to modify TiO 2 -based photocatalyst to extend the light absorption spectrum from the UV to VL region by elements doping, 2 noble metal deposition, 3,8 12 Despite the noticeable progress, these VLD photocatalysts still have some drawbacks, such as relatively low VL photocatalytic activity and poor stability, limiting their practical applications. It is therefore highly desirable to develop highly efficient VLD photocatalysts that could meet the needs for applications in environmental and energy fields.Currently, the localized surface plasmon resonance (SPR) effect of noble-metal nanoparticles (e.g., Ag and Au) has become a research focus in the development of VLD photocatalysts. 13 The VL activity of plasmonic photocatalyst is originated from the distinctive plasmon resonance effect in VL region that has been well demonstrated for metallic Au and Ag nanoparticles. 4,14−19 Also a number of Ag/AgX (X = Cl, Br)-based materials, such as graphene sheets grafted Ag/AgCl, 1 graphene oxide (GO) enwrapped Ag/AgX (X = Cl, Br) nanocomposite, 16 Ag/AgBr@TiO 2 , 18 Ag/AgCl@H 2 WO...

Visible-light-driven photocatalytic inactivation of E. coli by Ag/AgX-CNTs (X=Cl, Br, I) plasmonic photocatalysts: Bacterial performance and deactivation mechanism

“…The time required for complete inactivation of 1.5 × 10 7 cfu mL −1 of E. coli was extent to 50 and 60 min by Ag/AgCl-CNTs and Ag/AgI-CNTs, respectively. The order of photocatalytic disinfection activity is consentience with photocatalytic degradation of 2, 4, 6-tribromophenol reported in our previous study [30]. In addition, a study reported that Ag + at high concentration exhibited bactericidal activity [31].…”

“…The CNTs were pretreated by refluxing in the mixture of concentrated H 2 SO 4 acid (95-98%) and HNO 3 (65-68%), and the Ag/AgX-CNTs photocatalysts were prepared by an ultrasonic assistant deposition-precipitation method according to our previous study [30]. The crystal phase composition, surface chemistry properties as well as surface structure of the photocatalysts before and after used were characterized by X-ray diffraction (XRD, Rigaku Dmax 2200 V X-ray diffractometer), X-ray photoelectron spectroscopy (XPS, S-520/INCA 300 spectrometer using 300 W Mg-K␣ radiation, and the binding energies were referenced to the C1s line at 284.8 eV from adventitious carbon) and the Fourier transform infrared spectroscopy (FTIR, Bruker EQUINOX55 spectrometer).…”

“…It is of significance for the application of SPR photocatalysts to understand photocatalytic mechanisms of such Ag/AgBr-CNTs photocatalyst. To understand the band structure of AgBr phase, the conduction band (CB) and valence band (VB) energies of AgBr are calculated to be about −0.065 and +2.625 V (vs SHE), respectively [30]. Therefore, it is possible that the plasmon-induced electrons at Ag nanoparticles of Ag/AgBr-CNTs with a strong reduction power can readily transfer to CB (−0.065 V vs SHE) of AgBr [30].…”

“…To understand the band structure of AgBr phase, the conduction band (CB) and valence band (VB) energies of AgBr are calculated to be about −0.065 and +2.625 V (vs SHE), respectively [30]. Therefore, it is possible that the plasmon-induced electrons at Ag nanoparticles of Ag/AgBr-CNTs with a strong reduction power can readily transfer to CB (−0.065 V vs SHE) of AgBr [30]. The photocatalytic reaction is initiated by the absorption of VL photons, leading to the generation of electron-hole pairs derived from both photo-excited AgBr and plasmon-excited Ag nanoparticles (Eqs.…”

Regulations of silver halide nanostructure and composites on photocatalysis

“…While incorporation of AgX in high specific surface area substrate is another promising strategy in photocatalytic activity promotion, especially in wastewater treatment [322][323][324][325][326]. With the substrates as dispersing templates, homogeneous and uniform semiconductor crystal morphology could be formed, which in turn can enhance their photocatalytic performance [327][328][329][330][331][332][333][334]. The graphene sheets with high optical transmittance, large 2D specific surface area, unique electronic properties and locally conjugated aromatic system has regarded as one kind of ideal substrate candidates for photocatalytic deposition.…”