TiO2/carbon fiber composite is achieved by loading TiO2 nanoparticles on biomass carbon fiber, which originates from the carbonized natural bast. The carbonized process and the loading amount of TiO2 are researched in detail. It is found that the carbonized bast fiber shows robust adsorption characteristics for TiO2 nanoparticles in aqueous dispersion, and TiO2 nanoparticles with ~15 wt.% in total weight are uniformly loaded onto the fiber surface. The photocatalytic properties of TiO2/carbon fiber composite are evaluated by photocatalytic degradation of rhodamine B and water splitting for hydrogen production. The results indicate that 90% RhB molecules could be attacked in 60 min under UV light irradiation, and the hydrogen production rate of water splitting is up to 338.51
Since Fujishima and Honda reported the groundbreaking research work on splitting water to produce hydrogen on TiO2 electrode [
Carbon fiber is a kind of one-dimensional carbon material with excellent properties, such as high tensile strength, low weight, high chemical resistance, high temperature tolerance, and excellent electrical conductivity, making them very popular in many fields. However, commercialized carbon fiber is relatively expensive due to the raw materials and fabrication process, which is not conducive to the photocatalyst application in the wide range. Biomass fiber carbonization is a feasible route to obtain low-cost carbon fiber, which can meet some applications with no high requirement on mechanical behavior, such as photocatalyst and solar cells.
In the liquid phase system, TiO2 nanomaterials are difficultly recycled after reaction; the poison and aggregate of TiO2 powder are also disadvantageous factors [
Natural bast fiber was used in textile in the ancient times. Its main component is cellulose, which takes up about 75% content of the fiber. The bast becomes a kind of high-strength, low elongation fiber, so it is an ideal raw material of biomass carbon fiber. However, the electrical conductivity, high temperature resistance, and the chemical and physical adsorptions of bast fiber are disadvantageous. Biomass fiber carbonization is a suitable way to improve electrical conduction and structural properties, including increasing porous structure and fiber roughness, which are conducive to enhance the adhesion and load amount of TiO2 nanomaterials on the surface of biomass carbon fiber. Because bast fiber is widely accessible and low cost, the biomass carbon fiber using bast fiber as a raw material has great advantages in practical application of catalyst carrier.
Here, the bast was carbonized to get biomass carbon fiber. Then, the carbon fiber was put into TiO2 nanoparticle dispersion with different concentrations to obtain optimal TiO2/carbon fiber composite. Using the recycled photocatalyst, the photocatalytic degradation of rhodamine B (RhB) and water splitting for hydrogen production were performed, 90% RhB molecules were attacked in 60 min under UV light irradiation, and the hydrogen production rate was up to 338.51
TiO2/carbon fiber composites were prepared by the following process. A certain amount of bast fiber was located into the tube furnace. In the hydrogen ambience with 100 sccm, the fiber was heated to 300°C at a rate of 10°C/min and then maintained for 1.5 h. The biomass carbon fiber was obtained after cooling down. Different amounts of TiO2 nanoparticles (P25) were dispersed into 50 mL deionized water with strong ultrasonic to attain homogenous dispersion (5, 10, 15, and 20 g/L, resp.). After immersing the biomass carbon fiber into TiO2 dispersion for several minutes, the composites were annealed at 450°C under H2 ambience. TiO2/carbon fiber composites with different concentrations of TiO2 dispersions, labelled as TCF05, TCF10, TCF15, and TCF20, could be achieved by repeating the above-depicted procedures to increase the load amount. The load amount of TiO2 nanoparticles was estimated to be about 15 wt.% in total mass.
The morphology of the samples was characterized by field emission scanning electron microscopy (FESEM, Hitachi S4800). Raman spectroscopy (Horiba Jobin Yvon LabRAM HR800) and grazing-angle X-ray diffraction (Rigaku D/MAX-2400) were employed to characterize the crystal structure of the samples. UV-visible absorption spectrum was recorded using Hitachi U-3900H spectrophotometer to evaluate the photocatalytic degradation performance. Water splitting for hydrogen production was applied to evaluate the photocatalysis on photocatalytic hydrogen production system (Labsolar-IIIAG, Perfectlight Technology Co. Ltd., China).
The photocatalytic activities were evaluated by photodegradation of RhB molecules. The procedures had been reported in the previous works [
0.15 g TiO2/carbon fiber composite was added into the solution mixed by 90 ml water and 10 ml methanol. 2.5
Figures
The Raman spectrum (a) and SEM image (b) of biomass carbon fiber.
Figure
XRD patterns (a) and Raman spectra (b) of TiO2/carbon fiber micronanocomposites.
Figure
(a–d) SEM images of TCF05, TCF10, TCF15, and TCF20.
Figure
(a) The photocatalytic degradation of RhB with different TiO2/carbon fiber micronanocomposites under UV light irradiation. (b) Absorption spectral changes of RhB solution under UV light irradiation in the presence of TCF15. (c) The degradation kinetic data of RhB under UV light irradiation at different sampling time (d). Degradation rate
Here, C is the concentration of RhB and K is a constant. When the initial concentration of reactants is low, the formula can make the appropriate mathematical transform:
Here, C0 represents the initial concentration of RhB and C is the concentration of RhB after irradiation t min. This formula is a reaction kinetic equation. It is found that TiO2 photocatalytic degradation reactions abide by the first-order reaction kinetic equation [
To characterize the stabilization of the photocatalysis properties, TCF15 is done in the cycle test for photocatalytic degradation of RhB molecules (Figure
(a) The cycle test of TCF15 for photocatalytic degradation of RhB under UV light irradiation. (b) Absorption spectral changes of RhB solution under UV light irradiation in the presence of TCF15. (c) The degradation kinetic data of RhB under UV light irradiation at different cycle times. (d) Degradation rate
Besides the photocatalytic degradation of organic molecules, water splitting for hydrogen production is another excellent property of photocatalyst. The TiO2/carbon fiber composite can also be used to produce hydrogen energy. Figure
The hydrogen production of the TCF15 under UV light irradiation.
The above-depicted results indicate that TiO2/carbon fiber composite has the superior photocatalytic degradation of RhB molecules and water splitting for hydrogen production. To check the reliability of the composite, XRD and SEM are carried out on the TCF15 sample after performing the photocatalysis experiments. In Figure
XRD pattern (a) and SEM (b) image of TCF15 after the photocatalytic degradation cycle. (c, d) Photocatalytic reaction mechanism diagram.
Based on the above experimental results, a model is proposed to explain the photocatalytic mechanism of TiO2/biomass carbon fiber composite. Figure
As the raw material, natural bast fiber is carbonized to get biomass carbon fiber. TiO2/carbon fiber composites are achieved by combining biomass carbon fiber and TiO2 nanoparticles with anatase and rutile mixed phase. Based on the superior adsorbability and electrical conduction of the biomass carbon fiber, the composites show the excellent catalytic activities on photocatalytic degradation and water splitting for hydrogen production. The rate of photocatalytic hydrogen production can reach 338.51
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
This work was supported by a grant from the Fundamental Research Funds for the Central Universities (Grant no. 31920170036) and the State Key Laboratory of Advanced Processing and Recycling of Non-Ferrous Metals, Lanzhou University of Technology (SKLAB02014003).