Origin of the enhanced visible-light photocatalytic activity of CNT modified g-C3N4 for H2 production

Abstract

Graphitic carbon nitride (g-C3N4) hybridized with a small number of multi-walled carbon nanotubes (CNT) was synthesized using cyanamide as precursor. The optimal CNT content is found to be ∼0.2 wt% in the composite, which displays a 2.4-fold enhancement in photocatalytic water splitting over pure g-C3N4. Characterizations by a series of joint techniques including Raman spectra, UV/vis diffuse reflectance spectra, steady and time-resolved fluorescence emission spectra, and photocurrent responses were carried out, aiming to reveal the determinative factor for the improved visible-light response. Our results indicate that the increased photoactivity originates from the enhanced charge-transfer effect due to the intimate interactions between g-C3N4 and conjugated CNT. The presence of CNT in the hybrids is beneficial for improving electron-hole separation on the excited g-C3N4 by prolonging the lifetimes of charge carriers and improving the population distribution of short-lived and long-lived charge carriers.

g‐C3N4‐Based Heterostructured Photocatalysts

“…Platinum as the most efficient cocatalyst for H 2 generation has been most commonly used for enhancing the performance of gC 3 N 4 based heterostructured photocatalysts, [85,95,[228][229][230][231][232][233][234][235][236] and the role of noble metals, especially Pt, has been widely investigated. Fina et al [237] found that the crystallinity and distribution of Pt NPs on the surface of gC 3 N 4 greatly influ enced the photo catalytic activity of Pt/gC 3 N 4 .…”

“…Bimetallic cocatalysts such as PtCo, [205] PdAu, [239] PtOAu [240] have exhibited higher H 2 photocatalytic activity than single noble metals. So far, numerous nonnoble metal cocatalysts have proven efficient in enhancing the photo catalytic H 2 generation activity of gC 3 N 4 , including FeO x , [228] MoS 2 , [229,[241][242][243][244] WS 2 , [245] NiS, [246][247][248] Ni 12 P 5 , [249] carbon nanotube (CNT), [232] carbon black, [233] carbon nanofiber, [222] Co(OH) 2 , [250] Ni(OH) 2 , [251,252] Cu(OH) 2 , [253] Ni(dmgH) 2, [254] and Ni [208,255,256] (Table 3). So far, numerous nonnoble metal cocatalysts have proven efficient in enhancing the photo catalytic H 2 generation activity of gC 3 N 4 , including FeO x , [228] MoS 2 , [229,[241][242][243][244] WS 2 , [245] NiS, [246][247][248] Ni 12 P 5 , [249] carbon nanotube (CNT), [232] carbon black, [233] carbon nanofiber, [222] Co(OH) 2 , [250] Ni(OH) 2 , [251,…”

Hybridization of Cd0.2Zn0.8S with g-C3N4nanosheets: a visible-light-driven photocatalyst for H2evolution from water and degradation of organic pollutants

“…40,41 The broad peak centered at 3250 cm −1 can be assigned to the stretching mode of the N-H bond. 42 The FT-IR 10 spectrum of CZSCN20 shows weak peaks at 663, 970, 1630, 2360 and 3440 cm −1 , which is similar to the FT-IR spectrum of the pristine Cd 0.2 Zn 0.8 S. In addition, all the characteristic peaks of g-C 3 N 4 are observed in the CZSCN20 sample, confirming that the composite is composed of g-C 3 N 4 and Cd 0.2 Zn 0.8 S. XPS was used to analyze the surface chemical composition of g-C 3 N 4 , Cd 0.2 Zn 0.8 S and Cd 0.2 Zn 0.8 S/g-C 3 N 4 and to further study the interaction of Cd 0.2 Zn 0.8 S with the g-C 3 N 4 support. The survey spectrum of CZSCN20 (Fig.…”

Carbonyl‐Grafted g‐C3N4 Porous Nanosheets for Efficient Photocatalytic Hydrogen Evolution

“…Since Wang et al reported graphitic carbon nitride( g-C 3 N 4 ), am etal-free polymer semiconductor that is able to produce hydrogen or oxygen by splitting water under visible-light irradiation, [17] g-C 3 N 4 has attracted more and more attention for its application in supercapacitors, [18] lithiumion batteries, [19] photodegradation of pollutants, [20,21] and especially in photocatalytic hydrogen production. [26] Up to now,s everal approaches have been explored to improve the visible-light utilization of g-C 3 N 4 to achieve high photocatalytic activity,i ncluding doping with metal and/or nonmetal ions, [27][28][29][30][31][32] construction of heterojunctions with other semiconductors, [20,21,25,[33][34][35] copolymerization with organic molecules, [35][36][37][38][39] modification with carbon materials, [40][41][42] co-catalyst deposition, [43,44] thin-film fabrication, [45] and photosensitization with dyes. However, pristine g-C 3 N 4 exhibits limited photocatalytic activity owing to its small specific surface area, poor visible-light utilization, and fast recombination of photogenerated electrons and holes.…”