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Green Technology

Nano-material Synthesis and Its Environmental Applications

We employ a rapid, energy frugal and environmental friendly method to synthesize nitrogen doped titanate nanotubes (NTNTs), and use TEM, XRD, Raman, Nitrogen adsorption-desorption isotherms analysis, and UV-vis spectroscopy to characterize the obtained NTNTs. TEM results demonstrate that the current research successfully synthesized one-dimensional NTNTs via the microwave hydrothermal (M-H) method, and show that NTNTs retain a tubular structure after sintering at a temperature of 350 ℃. XRD results agree well with Raman spectrum findings. Both show that the intensity of anatase crystallization increases with an increase in sintering temperature. After sintering at high temperature, above 250 ℃, the UV-Vis absorbance edges of NTNTs significantly shift to the visible-light region, which illustrates N atom doping into nanotubes. Photocatalytic tests conclude that the NTNTs-350 shows good efficiency with visible light response.​

  • Y.P. Peng, S.L. Lo, H.H. Ou, S.W. Lai, 2010. Microwave-assisted hydrothermal synthesis of N-doped titanate nanotubes for visible-light-responsive photocatalysis. Journal of  Hazardous Materials, 183, 754 - 758. (SCI, IF=4.14)

  • 彭彥彬、駱尚廉、 賴孝武、陳谷汎，「Microwave-assisted hydrothermal synthesis of N-doped titanate nanotubes for visible-light-responsive photocatalysis」，2012環境保護與奈米科技學術研討會，高雄大學，高雄，台灣，2012。

Photoelectrochemical Degradation of Pollutants

We investigated the synergetic effect of electrochemical and photocatalytic oxidation in photoelectro-chemical (PEC) process for the degradation of hazardous organic compounds exemplified by methyl orange, an azo dye. Nitrogen doped TiO2 thin film (NTTF) synthesized by the pulsed laser deposition (PLD) method, was used as the working anode. The crystalline, optical properties, surface morphology, and structure of the NTTF were characterized by XRD, UV–vis absorbance edges, SEM, and XPS. Results showed that the NTTF was dominated by anatase phase after sintered at 600 oC with significant visible light response at 595 nm. XPS analyses indicated nitrogen doping was mainly responsible for reducing the band gap as evidence of 3% N doping into the structure via the linkage of Ti O N and N Ti O bond. SEM images illustrated the nitrogen-doped TiO2 nanoparticles being attached firmly and spread evenly over the ITO glass surface, which is beneficial for PEC applications. The degradation efficiency of MO by pho-toelectrochemical, photocatalytic, electrochemical and photolysis methods were compared in terms of pseudo-first-order reaction rate. PEC was the most efficient in degrading MO at a bias potential of 2.0 V (vs. SCE) under light at a wavelength of 325 nm, which was consistent with results of IPCE (%) measurements. The synergetic effect was quantified at current/bias potential of 0.07 mA/0.3 V and 0.6 mA/2.0 V, respec-tively. Results demonstrated that the bias potential could separate photogenerated holes and electrons effectively and enhance the electrochemical-oxidation of MO. The mechanistic aspects of MO degradation by the PEC process were discussed.

 

  • Yen-Ping Peng, Emre Yassitepe, Yun-Ta Yeh, S. Ismat Shah, Chin-Pao Huang, Inci Ruzybayev, 2012, Photoelectrochemical Degradation of Azo Dye at Pulsed Laser Deposited Nitrogen-doped TiO2 Thin Film. Applied Catalysis B: Environment, 125, 465-472.

  • Yen-Ping Peng, Yun-Ta Yeh, Emre Yassitepe, Ismat Shah, Chin-Pao Huang, 2011. The Removal of Hazardous Chemicals from Water Using Solar-energy Driving Nitrogen-doped TiO2 Thin Films. Tri - Association Annual Conference. Ocean City, MD, USA.

Photoelectrochemical Reduction of Carbon Dioxide 

This study employed a novel material, nitrogen doped TiO2 thin film (NTTF), as a photoanode for the concurrent photoeletrochemical (PEC) reduction of CO2 and oxidation of methyl Orange (MO).  Under illumination, the onset potential of the total current was approximately 1.5 V (vs. SCE) and the maximum total current was around 0.65 mA at 2 V (vs. SCE). The photocurrent can be effectively driven to the counter electrode at this positive potential, which will decrease the recombination of photo-generated holes and electrons, leading to more electrons available for CO2 reduction in the cathodic chamber and more holes for the oxidation of hazardous chemicals in the anodic chamber simultaneously. Formic acid, formaldehyde, methanol and methane were detected as the CO2 reduction products at a Cu electrode in the KHCO3 electrolyte. The first-order kinetic model was successfully applied to simulate the NTTF PEC reduction of CO2. The reaction rate constant were 6.68×10-7, 2.18×10-4, 8.62×10-4 and 2.27×10-4 s-1, for the formation of formic acid, formaldehyde, methanol, and methane, respectively. The maximum Faradaic efficiency was 5.01, 1.04, 5.41 and 7.83% for the generation of formic acid, formaldehyde, methanol, and methane, individually.  In addition, the effect of initial CO2 concentration on CO2 reduction was also conducted in the presence of methanol (0, 20 and 40%). Results showed that methanol-containing electrolyte enhanced CO2 solubility thereby suppressing hydrogen generation and favoring CO2 reduction. Finally, the degradation of methyl orange was compared using PEC, photocatalytic (PC), electrochemical (EC) and direct photolysis (P) processes. The PEC process was able to achieve a 10-log versus less than 1-log of methyl orange degradation by all other methods studied within 60 min under otherwise similar conditions of pH, temperature, intensity and wavelength of light source.  Results clearly demonstrated the potential of a sustainable technology for the concurrent reduction of CO2 and oxidation of hazardous chemicals by the PEC process using solar energy. 

 

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  • Yen-Ping Peng, Emre Yassitepe, Yun-Ta Yeh, S. Ismat Shah, Chin-Pao Huang, Po-Yen, Wang, 2012, Photoelectrochemical Reduction of Carbon Dioxide via Nitrogen-doped TiO2 Thin Film. Applied Catalysis B: Environment, 123-124, 414-423.

  • Yen Ping Peng, Chin Pao Huang, YunTa Yeh, S. Ismat Shah, 17-19, July, 2012. Photoelectrochemical Reduction of Carbon Dioxide via Nitrogen-doped TiO2 Thin Film. Sustainable Water Environment International Conference. Guilin, China.

Photoelectrochemical Process for the Concurrent Reduction of Carbon Dioxide and Degradation of Azo Dye 

We studied CO2 reduction using a solar cell driven photoelectrochemical (PEC) reactor in dilute aqueous KHCO3 (0.1 M) solution.  Results show that CO2 was reduced to four major hydrocarbon species, namely, formic acid (HOOH), formaldehyde (HCOH), methanol (CH3OH), and methane (CH4).  Over a reaction time of 5 h, the product yield was 1.55, 0.62, 2.02, and 2.16 µM with a current efficiency of 0.22, 0.17, 0.84 and 1.2 %, for HCOOH, HCOH, CH3OH, and CH4, respectively, whereas hydrogen, produced from water electrolysis, exhibited the highest current efficiency of 56.66%.  It is also noted that the production of organic carbons was enhanced by increasing the CO2 concentration due to the presence of methanol.  Results showed that methanol hindered hydrogen formation and increased the yield of organic carbons.  Furthermore, the degradation of an azo dye, namely, methyl orange (MO) was observed using PEC process under different applied currents.  The degradation rate was increased by two orders of magnitude when a bias potential was applied to the solar cell system. Our results demonstrated the potential of solar energy for CO2 conversion to energy-rich organic carbons and the remediation/purification of impaired water. ​

  • Yen-Ping Peng, Yun-Ta Yeh, Chin-Pao Huang, Po-Yen, Wang, 2013. A Solar Cell Driven Photoelectrochemical Process for the Concurrent Reduction of Carbon Dioxide and Degradation of Azo Dye in Dilute KHCO3 Electrolyte. Separation and Purification Technology, 117, 3-11.

Green Synthesis of Nano-material for Concurrent Pollutant Degradation and Hydrogen Generation in Photoelectrochemical Process

Silver deposited titanate nanotube array composite (Ag/TNA-c) was successfully synthesized using tea leaves and ground coffee as reducing agent for the first time. The synthesis method was effective, ecofriendly, and reproducible in producing quality nano-composite. The Ag/TNA composite was characterized via XPS, SEM, UVevis, XRD, and electrochemical analyses for chemical and physical properties. Additionally, chlorogenic acid, caffeine, and catechin were selected as reducing agents for purpose of comparison. Results indicated that catechin and chlorogenic acid were the main reducing agents responsible for Agþ reduction in tea leaves and ground coffee, respectively. The synthesized Ag/TNA-c exhibited the best photocatalytic (PC) performance in terms of photo-current response, EIS, Ibuprofen degradation, and hydrogen generation in a PEC system. Pairing with a Pt cathode, the photoelectrochemical (PEC) system using the synthesized Ag/TNA composite photo-anode, was capable of concurrent anodic oxidation of Ibuprofen and cathodic generation of hydrogen. Deposition of nano-Ag particles on TNA enhanced the concurrent oxidation and reduction reaction in the PEC system. Results of ESR analysis confirmed the role of hydroxyl radical on Ibuprofen degradation over Ag/TNA-c in the PEC system. Mechanism of Ag/TNA PEC system was proposed to illustrate the oxidation and reduction reaction.

  • Peng, Y. P.*, Liu, C. C., Chen, K. F., Huang, C. P., Chen, C. H. (2021). Green synthesis of nano-silver–titanium nanotube array (Ag/TNA) composite for concurrent ibuprofen degradation and hydrogen generation. Chemosphere, 264, 128407.

This study aimed to produce a clean energy, hydrogen, and to remove pollutants simultaneously in water by photoelectrochemical (PEC) method. The photo-anode of cuprous oxide modified titanate nanotube arrays (Cu2O/TNTAs) was synthesized by using lactic acid, green tea, and coffee as reductants individually. The characterizations of Cu2O/TNTAs were performed by ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), field emission scanning electron microscope (FE-SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) to investigate the physical and chemical properties such as structure, crystallization, element contents, and optical performance. The electrochemical analyses of Cu2O/TNTAs showed the photo-current of Cu2O/TNTAs-t (using green tea as reductant) was 2.4 times higher than pure TNTAs, illustrating the effective separation of electron-hole pairs after Cu2O modification. The photoelectrochemical performances of Cu2O/ TNTAs-t and Cu2O/TNTAs-c (using coffee as the reductant) were better than Cu2O/TNTAs-L (using lactic acid as the reductant) in terms of photo-current density, Ibuprofen degradation, and hydrogen generation, implying that depositing Cu2O on TNTAs can significantly improve the electron mobility by reducing the recombination rate of electron-hole pairs, which is beneficial to simultaneously ibuprofen degradation and hydrogen production.

  • Chen, C. H., Lin, Y. C., Peng, Y. P.*, Lin, M. H. (2021). Simultaneous hydrogen production and ibuprofen degradation by green synthesized Cu2O/TNTAs photoanode. Chemosphere, 284, 131360.

In this study, electrodes of titanium dioxide nanotube arrays (TNAs) were successfully synthesized by applying the anodic oxidation etching method, as well as the use of green synthetic technology to add reducing agents of tea or coee to reduce metal palladium from palladium chloride. Synthesis of palladium modified TNAs (Pd/TNAs) was conducted by the microwave hydrothermal method after the metal palladium was reduced. In order to identify the surface structure, light absorption and elemental composition, TNAs and Pd/TNAs were characterized by X-ray photoelectron spectroscopy (XPS), and X-ray diraction (XRD). Furthermore, to test the photocurrent density, electron resistance, and hydroxyl radicals by I-t plot, electrochemistry impedance spectroscopy (EIS), and electron paramagnetic resonance (EPR) were investigated. The photocurrent (4.0 mA/cm2) of Pd/TNAs-C (using coffee as the reducing agent) at +1.0 V (vs. Ag/AgCl) was higher than that of the pure TNAs (1.5 mA/cm2), illustrating that Pd/TNAs-C can eectively separate photogenerated electrons and holes. Pd/TNAs is a favorable material as a photoanode for the photoelectrochemical (PEC) removal of organic pollutants in wastewater.

  • Lin, Y. C., Chen, C. H., Chen, K. S., Peng, Y. P.*, Lin, Y. C.*, Huang, S. W., Huang, C.E., Lai, H.W., Li, H. W. (2020). Green synthesized palladium coated titanium nanotube arrays for simultaneous azo-dye degradation and hydrogen production. Catalysts, 10(11), 1330.

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