Enhancement of Visible Light-Responsive Photocatalytic Efficiency by Using a Laccaic Acid-Modified Titanium Dioxide Photocatalyst

Abstract

In this study, a laccaic acid-modified TiO₂ photocatalyst (Lac-TiO₂) was prepared via an impregnation method with 0.50, 1.00, 2.50, and 5.00 wt.% laccaic acid. The products’ physical properties were examined through X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoemission spectroscopy (XPS), UV-Vis diffused reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption/desorption, and photoluminescence (PL) spectroscopy. A possible photocatalytic mechanism was also proposed. XRD patterns revealed the anatase phase of TiO₂ and Lac-TiO₂ samples. High-magnification FE-SEM images showed that the TiO₂ and Lac-TiO₂ samples exhibited spherical-like structures. XPS results complementarily confirmed the presence of Ti, O, and C as the main elements of the Lac-TiO₂ samples. Interestingly, the DRS spectra of the Lac-TiO₂ samples extended into the visible region. FTIR spectra presented the characteristic bands of TiO₂ and hydroxyl groups on the TiO₂ surface. Instead of hydroxyl groups, the characteristic bands of laccaic acid were observed on the surface of the Lac-TiO₂ samples. The photocatalytic properties of the Lac-TiO₂ samples were evaluated in terms of methyl orange degradation under visible light irradiation. The Lac-TiO₂ samples showed higher photocatalytic performance than the TiO₂ sample.

Keywords:
TiO₂; laccaic acid-modified TiO₂; impregnation method; visible photocatalyst; degradation of methyl orange

Introduction

Photocatalytic oxidation has been widely explored in terms of the removal of contaminants, including toxic organic pollutants.¹-³ In this process, various substances, including semiconductor photocatalysts, are used.⁴ Among all kinds of semiconductor photocatalysts, titanium dioxide (TiO₂) is widely applied in heterogeneous photocatalysis because of its low price, nontoxicity, chemical stability, and high photocatalytic activity.⁵-⁷ However, the application of pure TiO₂ in photocatalysis is limited due to its wide band gap (3.2 eV) and fast recombination of photogenerated electron-hole pairs. Therefore, its activity under visible and solar light is restricted.⁸ To overcome these limitations, researchers developed several strategies, such as metal deposition,⁹,¹⁰ transition metal doping,¹¹-¹⁴ nonmetal doping,¹⁵-¹⁸ dye-sensitized TiO₂,¹⁹-²³ and coupling with other narrow-band gap semiconductors.²⁴-²⁶

Sensitization of TiO₂ particles with dye molecules is considered an efficient method to extend their photocatalytic property into the visible region.²⁷ Some common dye sensitizers include porphyrin,¹⁹ phthalocyanine,²¹ and natural dyes.²²,²³ In general, the mechanism for the TiO₂ photocatalyzed reaction involves the generation of electron-hole pairs through light illumination. The introduction of a dye-sensitizer allows visible light absorption due to the narrower band gap of the dye molecules. The photoexcited electrons of adsorbed dyes are then injected into the conduction band (CB) of the TiO₂ photocatalyst.¹⁹-²¹ Hydroxyl radical (•OH) and superoxide radical species (O₂^•-) are generated on the surface of the photocatalyst and then react with organic substances, hence the degradation.²⁸ In addition to light adsorption, the size, shape, surface area, morphological characteristics, and dimensionality of catalysts significantly affect their photocatalytic activity.²⁹,³⁰ The small size of TiO₂ nanoparticles provides a large surface area and facilitates the charge transfer process that prevents the recombination of the electron-hole pairs.³¹-³³

In the present work, laccaic acid-modified TiO₂ (Lac TiO₂) was prepared via an impregnation method. The effects of the amount of laccaic acid loaded on the TiO₂ surface on the microstructure, optical properties, and photocatalytic activity of Lac-TiO₂ were investigated. The synthesized Lac-TiO₂ samples were characterized by X-ray diffraction analysis (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), UV-Vis diffused reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), nitrogen adsorption/desorption, and photoluminescence (PL) spectroscopy. The photocatalytic activity of the as-prepared Lac-TiO₂ samples was tested and compared with a pure TiO₂ sample using methyl orange (MO) as a model pollutant. The hydroxyl radical (•OH) generated during the photocatalytic reaction was examined, and a possible mechanism was proposed.

Experimental

Materials

Titanium(IV) isopropoxide was obtained from Sigma-Aldrich (St. Louis, Missouri, USA). Ethanol (C₂H₅OH) was purchased from Merck (Darmstadt, Germany). Methyl orange and terephthalic acid were obtained from Sigma-Aldrich (Saint Louis, USA). Laccaic acid solutions were prepared from the insect nest (Laccifer lacca) received from a local market in Nakhon Pathom Province, Thailand. All chemicals were of analytical grade and used as received.

Preparation of TiO₂

TiO₂ was prepared by the sol-gel method. First, 10.00 mL of titanium(IV) isopropoxide were mixed with 90.00 mL of ethanol. The mixture was stirred at room temperature for 24 h and a white TiO₂ precipitate was obtained. The TiO₂ precipitate was filtered and washed with deionized water. The as-prepared TiO₂ powder was dried at 60 °C for 24 h.

Preparation of Lac-TiO₂ photocatalyst

In brief, Lac-TiO₂ was synthesized via an impregnation method. The as-prepared TiO₂ powder (0.50 g) was suspended in laccaic acid solution (50.00 mL) with different concentrations (0.50, 1.00, 2.50, and 5.00 wt.%) for 2 h. After impregnation, the Lac-TiO₂ precipitate was filtered, washed with ethanol, and dried at 80 °C for 12 h. The catalysts synthesized from 0.5, 1.0, 2.5, and 5.0 wt.% laccaic acid solutions were denoted as 0.5Lac-TiO₂, 1.0Lac TiO₂, 2.5Lac-TiO₂, and 5.0Lac-TiO₂, respectively. The synthesis route of Lac-TiO₂ is shown in Figure 1.

Figure 1
Synthesis route of Lac-TiO₂ via an impregnation method.

Characterizations

The crystal structures of the as-prepared pure TiO₂ and Lac-TiO₂ samples were determined through XRD recorded in a Rigaku MiniFlex II X-ray diffractometer (Singapore) with Cu Kα radiation (1.5406 Å) from 20° to 80° (2θ). Morphological characteristics were investigated via FE SEM (TESCAN model MIRA3) (Brno, Kohoutovice, Czech Republic). Chemical compositions were collected with XPS (a voltage of 15 kV, and an emission current of 10 mA) by using a Kratos Axis Ultra spectrometer (Manchester, UK) with a monochromic Al Kα source at 1486.7 eV. The optical absorption property and band gap energy were determined using a Shimadzu UV-2401 spectrophotometer (Tokyo, Japan). FTIR spectra were obtained with a PerkinElmer Spectrum Bx spectrophotometer (Waltham, Massachusetts, USA) in the range of 400-4000 cm^-1 via attenuated total reflectance (ATR). The surface area and pore diameter were measured by nitrogen adsorption/desorption using a Micromeritics ASAP 2460 surface area and porosity analyzer (Norcross, GA, USA). The specific surface areas were calculated by the Brunauer-Emmett-Teller (BET) and the pore volume and pore size were calculated by the Barrett-Joyner-Halenda (BJH) method.

Photocatalytic experiment

The photocatalytic activity of the as-prepared pure TiO₂ and Lac-TiO₂ was evaluated in the degradation of methyl orange (MO) under visible light. For each experiment, 0.05 g of the photocatalyst was suspended in 50 mL of MO (1.0 × 10^-5 M) in the dark for 1 h to allow the adsorption/desorption equilibrium between the photocatalyst and MO. The suspension was irradiated under 18 W fluorescence lamps (TL-D 18 W/865 Philips tube light).¹⁰,³⁴,³⁵ With stirring and irradiation, 5 mL of the suspension was collected every 60 min. The samples were centrifuged and the concentration of the remaining MO was analyzed using a UV-Vis spectrophotometer (Agilent HP model 8453, Victoria, Australia).

The photocatalytic efficiencies of the as-prepared pure TiO₂ and Lac-TiO₂ were measured by the following equation:

(1)$$\text{Photocatalytic efficiency}(\mathrm{\%})=\frac{{\mathrm{A}}_{\mathrm{i}}-{\mathrm{A}}_{\mathrm{t}}}{{\mathrm{A}}_{\mathrm{i}}}$$

where A_i is the initial concentration of MO, and A_t is the concentration of MO at pre-determined time intervals.

The amount of the hydroxyl radical generated during the photocatalysis was determined using terephthalic acid as an^•OH scavenger following previously described methods.²⁰,³⁶ The fluorescence emission spectra (excitation wavelength 315 nm) were measured on a PerkinElmer LS-50B luminescence spectrometer (Beaconsfield, UK).

Results and Discussion

Microstructure and optical property

The crystal structures of pure TiO₂ and Lac-TiO₂ were investigated by XRD. In Figure 2, all the samples showed a broad peak at 25.3° indicating the low amount of the anatase phase (JCPDS No. 21-1272) mixed with an amorphous phase.³⁷ After modification with different amounts of laccaic acid, no apparent change was observed in the XRD patterns. The XRD results suggested that the combination of TiO₂ and laccaic acid did not modify the crystal structure and the size of TiO₂.

Figure 2
XRD patterns of TiO₂ and Lac-TiO₂ samples.

The morphological characteristics of the as-prepared TiO₂ and Lac-TiO₂ were observed through FE-SEM (Figure 3). Titania crystals are highly agglomerated, becoming nearly spherical with size of approximately 100-200 nm for TiO₂-supporting materials. Lac-TiO₂ showed the same morphology as that of pure TiO₂ with the TiO₂ surface covered with laccaic acid molecules. The effect was more obvious when a high content of laccaic acid was present.

Figure 3
FE-SEM images of TiO₂ and Lac-TiO₂ samples.

The surface chemical composition and bonding configuration of TiO₂ and laccaic acid molecules in Lac-TiO₂ samples were investigated. The full-scale XPS analysis (Figure 4a) showed a Ti2p peak at 458.5 eV, an O1s peak at 532 eV, and a C1s peak at 284.8 eV for Lac TiO₂. This result indicated the existence of laccaic acid in Lac TiO₂. In Figure 4b, two individual peaks of Ti2p appeared at binding energies near 458.4 and 464.1 eV corresponding to Ti2p_3/2 and Ti2p_1/2, respectively. This result implied a Ti⁴⁺ oxidation state of the TiO₂ structure. For Figure 4c, four peaks of O1s were observed at the binding energies of 530.34, 531.54, 532.42, and 533.39 eV. These peaks corresponded to four different types of O species, which were possibly Ti-O bonds (the lattice oxygen of TiO₂), hydroxyl (^•OH) species, Ti-O-C bonds, and -COOH, respectively.³⁸-⁴⁰ For C1s spectra (Figure 4d), three main separated peaks were observed at 284.9, 286.5, and 289.2 eV and assigned to C-C/C=C bond (285.0 eV), C-O bond (286.6 eV), and C=O (288.8 eV), respectively.³⁸ Consistent with the data obtained from FE-SEM, the XPS results confirmed the existence of laccaic acid molecules in the Lac-TiO₂ samples.

Figure 4
(a) XPS survey spectra of Lac-TiO₂ samples and high-resolution spectra of the sample for (b) Ti2p; (c) O1s; and (d) C1s.

The optical properties of the as-prepared pure TiO₂ and Lac-TiO₂ samples were examined through DRS (Figure 5). The absorption band of Lac-TiO₂ samples showed an evident redshift to the visible light region.¹⁰,²⁰

Figure 5
DRS spectra of the prepared TiO₂ and Lac-TiO₂ samples.

The band gap (E_g) of the pure TiO₂ and Lac-TiO₂ samples were determined using equation 2:

(2)$${\mathrm{E}}_{\mathrm{g}}=\frac{\mathrm{h}\mathrm{c}}{\mathrm{\lambda }}=\frac{1240}{\mathrm{\lambda }}$$

where h is Plank’s constant (6.626 × 10^-34 J s), c is the velocity of light (3 × 10⁸ m s^-1), and λ is the wavelength (nm). The calculated band gap of all samples are shown in Table 1.

Table 1
Calculated band gap of the prepared TiO₂ and Lac-TiO₂ samples

TiO2 photocatalyst	Band gap / eV
TiO2	3.26
0.5Lac-TiO2	2.90
1.0Lac-TiO2	2.74
2.5Lac-TiO2	2.71
5.0Lac-TiO2	2.67

The energy gap decreased from 3.26 to 2.67 eV with increasing laccaic acid concentration. The presence of laccaic acid dye in the Lac-TiO₂ effectively increased the absorption in the visible light region suitable for applications employing solar light.

FTIR spectra of the pure TiO₂ and Lac-TiO₂ samples are shown in Figure 6. The broad bands at around 400 1000 cm^-1 were attributed to Ti-O-Ti bond vibrations.¹⁰,⁴¹ The peaks at 3000-3600 and 1640 cm^-1 suggested the presence of the surface-adsorbed H₂O.⁴¹,⁴² Moreover, the vibration bands of Ti-O-C bond observed at 1405 and 1439 cm^-1 in the Lac-TiO₂ samples indicated that laccaic acid molecules were adsorbed on TiO₂ surface.⁴¹,⁴²

Figure 6
FTIR spectra (ATR) of TiO₂ and Lac-TiO₂ samples.

Photocatalytic activity

Typically, photocatalytic degradation involved two processes: adsorption of pollutant molecules on the catalyst and the photocatalytic process. The adsorption of MO measured in the dark of the as-prepared pure TiO₂ and Lac-TiO₂ samples were approximately 20 and 8-10%, respectively. All Lac-TiO₂ samples showed a lower adsorption percentage than pure TiO₂ possibly due to the electrostatic repulsion between the negatively charged laccaic acid and MO under the condition studied (pH = 7). Once the adsorption/desorption equilibrium of MO had been established, the photocatalytic degradation of MO using the as-prepared pure TiO₂ and Lac-TiO₂ samples was examined under visible light irradiation. The results revealed the higher photocatalytic activity of the Lac-TiO₂ (0.5-2.5 wt.%) than that of the pure TiO₂ (except 5.0Lac TiO₂) (Figure 7). An optimum amount of laccaic acid on the TiO₂ surface should be considered. Although more laccaic acid loading might provide a better visible-light-harvesting ability, the amount of laccaic acid present on the surface of the photocatalyst can affect its number of active sites. In a photocatalytic process, the oxidant species (O₂^•- and^•OH) generated by the photo-excited electrons at the surface of the catalysts reacted with the adsorbed dyes, hence the active sites lied on the surface and microstructure of the catalyst. The 1.0Lac-TiO₂ sample showed the highest photocatalytic activity. The higher loading of laccaic acid (2.5 and 5.0 wt.%) did not yield a better photocatalytic activity. The lower photocatalytic discoloration percentage of the higher-loading Lac-TiO₂ was attributable to high laccaic acid adsorbed on the surface leading to loss of active sites for generating oxidants species (O₂^•- and^•OH).²⁹-³² The specific surface area of the as-prepared pure TiO₂ and 1.0Lac-TiO₂ samples were measured by nitrogen adsorption-desorption isotherms. The 1.0Lac-TiO₂ contained a greater surface area (386 m² g^-1, with pore size diameter around 26 nm) than that of pure TiO₂ (340 m² g^-1, with pore size diameter around 30 nm)(Figure 8). The greater surface area of 1.0Lac-TiO₂ supported the greater photocatalytic activity over pure TiO₂ due to more active sites available.

Figure 7
Comparison of the photodegradation efficiencies of MO by using TiO₂ and Lac-TiO₂ samples under visible light irradiation.

Figure 8
Nitrogen adsorption-desorption isotherms of pure TiO₂ and 1.0Lac-TiO₂ samples.

The hydroxyl radicals (^•OH) generated by the TiO₂ photocatalyst are very powerful oxidants and play a role in the degradation of organic pollutants.²⁴ The fluorescence technique was used to monitor the^•OH generated during the photooxidation process. Terephthalic acid, an^•OH scavenger, was transformed into 2-hydroxyterephthalic acid observed by the presence of a fluorescence emission peak at 424 nm. The results showed that the amount of 2-hydroxyterephthalic acid was proportional to the irradiation time suggesting that^•OH was generated during the reaction. The amount of^•OH detected from the reaction samples photocatalyzed by 1.0Lac-TiO₂ was greater than that of the as-prepared pure TiO₂ (Figure 9), consistent with the greater photocatalytic activity of 1.0Lac-TiO₂.

Figure 9
Comparison of the amount of^•OH radicals produced during photocatalysis using (a) pure TiO₂ sample and (b) 1.0Lac-TiO₂ sample under visible light irradiation.

A comparison of the photoluminescence emission spectra of the pure TiO₂ sample and the 1.0Lac-TiO₂ sample was shown in Figure 10. Both samples showed a low emission peak around 650-665 nm (excitation wavelength 550 nm). The 1.0Lac-TiO₂ sample exhibited a lower emission intensity than that of the pure TiO₂ sample. This result was consistent with the above-mentioned result on the amount of hydroxyl radical generated since the emission arose from the electron-hole recombination. The more intense emission of the pure TiO₂ sample indicated more recombination, hence less^•OH generated. The modification of the catalyst with laccaic acid led to more efficient separation of the photogenerated electron-hole pairs, hence more^•OH generated and higher photocatalytic efficiency.

Figure 10
Photoluminescence emission spectra of pure TiO₂ and 1.0Lac-TiO₂ samples.

Photocatalytic activity is influenced by light adsorption, adsorption of oxygen and pollutants on the surface of the catalysts, charge separation, and electron-hole pairs recombination. A possible photocatalytic mechanism of Lac-TiO₂ samples is shown in Figure 11. When illuminated with visible light, the laccaic acid electrons are excited and laccaic acid can act as an effective electron donor. The photo-excited electrons are injected into the CB of TiO₂. These electrons (e_CB^•- (TiO₂)) subsequently reduce the O₂ adsorbed on the TiO₂ surface to generate superoxide anion, O₂^•- which further transformed into H₂O₂ and then^•OH.⁴³,⁴⁴ As^•OH is a very strong and highly reactive oxidant, it reacts with organic substances such as MO and degrades it. The positively charged laccaic acid (laccaic acid⁺) may interact with surrounding solvent molecules (S) and return to the neutral stage that will be ready for the next round of excitation under visible light irradiation.⁴⁵-⁴⁷ The following equations represent the proposed mechanism:

(3)$$\text{laccaic acid}+\mathrm{h}\mathrm{v}\to \text{laccaic acid}\ast$$

(4)$$\text{laccaic acid}\ast +{\mathrm{T}\mathrm{i}\mathrm{O}}_2\to \text{laccaic acid}+{\mathrm{e}}_{\mathrm{C}\mathrm{B}}{}^{•-}\left({\mathrm{T}\mathrm{i}\mathrm{O}}_2\right)$$

(5)$${\mathrm{O}}_2(\mathrm{a}\mathrm{d}\mathrm{s})+{\mathrm{e}}_{\mathrm{C}\mathrm{B}}•-\left({\mathrm{T}\mathrm{i}\mathrm{O}}_2\right)\to {\mathrm{O}}_2^{•-}$$

(6)$${\mathrm{O}}_2^{•-}+{\mathrm{H}}^{+}\to {\mathrm{H}\mathrm{O}}_2^{\bullet }$$

(7)$$2{\mathrm{H}\mathrm{O}}_2{}^{•}+{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{H}}_2{\mathrm{O}}_2+{}^{•}\mathrm{O}\mathrm{H}$$

(8)$$\mathrm{M}\mathrm{O}+{}^{\circ }\mathrm{O}\mathrm{H}\to \text{degradation products}$$

(9)$$\text{laccaic acid}{}^{+}+\mathrm{S}\to \text{laccaic acid}+{\mathrm{S}}^{+}$$

Figure 11
Schematic of the photocatalytic activity of Lac-TiO₂ under visible light irradiation.

TiO₂ photocatalysts for the degradation of dyes in wastewater treatment

The developed photocatalyst with laccaic acid can be subjected to the discussion in comparison with other photocatalytic systems. Among various metal oxide semiconductors, TiO₂ is the most frequently employed photocatalyst. Although TiO₂ has good photocatalytic properties, its photocatalytic activity is limited by the tendency to have low absorption in the visible-light region and electron-hole recombination. To overcome these limitations, many methods have been developed. Table 2 shows information in association with different modifications of TiO₂ such as metal doping (Co-doped TiO₂),⁴⁸ non-metal doping (P-doped TiO₂),⁴⁹ and organic dye sensitization of TiO₂.⁵⁰-⁵³ Among these methods, dye-sensitized TiO₂ has gained interest owing to its stability and improved photocatalytic efficiency. Previous studies include the usage of metalloporphyrins,⁵⁰ tin(IV) porphyrin,⁵¹ zinc phthalocyanine,⁵² and subphthalocyanine-sensitized TiO₂,⁵³ which exhibited an enhanced visible-light photocatalytic activity as compared to the unsensitized TiO₂. Despite such interesting phenomena, the high cost and environmental toxicity of metal used in these metal-doped TiO₂ and dye-sensitizers hinder their widespread use in water treatment applications. Therefore, we developed a new laccaic acid-modified TiO₂ photocatalyst prepared by a simple, rapid and environmentally friendly approach. Our catalyst not only facilitates visible light absorption, providing a possibility for irradiation under solar light but also shows good photocatalytic properties. Due to those characteristics, the laccaic acid-modified TiO₂ could be a good candidate as a new dye-sensitized TiO₂ photocatalyst for the degradation of organic dyes in wastewater treatment.

Table 2
Preparation and photocatalytic properties of modified TiO₂

Photocatalyst	Phase	Light source	Amount of catalyst / g	Concentration of dye	Photocatalytic efficiency / %	Reference
Co-doped TiO2	anatase	visible	0.10	100 mL of MO (30 mg L-1)	Co-doped TiO2 (ca. 47%, 3 h) TiO2 (ca. 20%, 3 h)	48
P-doped TiO2	anatase	visible	0.01	10 mL of MO (20 mg L-1)	P-doped TiO2 (ca. 84%, 8 h)	49
Metalloporphyrins (MP)-sensitized TiO2	75% anatase and 25% rutile	visible	0.04	150 mL of MO (20 mg L-1)	CuP-TiO2 (ca. 33%, 3 h) > MnP-TiO2 (ca. 23%, 3 h) > TiO2 (ca. 5%, 3 h)	50
Tin(IV) porphyrin-sensitized TiO2	75% anatase and 25% rutile	visible	0.01	10 mL of MO (1.0 × 10-4 M)	SnP-TiO2 (ca. 85%, 3 h) > TiO2 (ca. 5%, 3 h)	51
Zinc phthalocyanine-sensitized TiO2	anatase	near visible	0.04	30 mL of MO (10 mg L-1)	ZnPc-TiO2 (ca. 60%, 2.5 h) > TiO2 (ca. 35%, 2.5 h)	52
Subphthalocyanine (H12SubPcB‑OPh2OH)-sensitized TiO2	anatase	UV	0.05	50 mL of MO (10 mg L-1)	H12SubPcB-OPh2OH -TiO2 (ca. 96%, 3 h) > TiO2 (ca. 29%, 3 h)	53
Our system (Lac‑TiO2)	anatase mixed with amorphous TiO2	visible	0.05	50 mL of MO (1.0 × 10-5 M)	1.0Lac-TiO2 (ca. 54%, 3 h and ca. 80%, 5 h) > P25‑TiO2 (ca. 32%, 3 h and ca. 52%, 5 h) > TiO2 (ca. 18%, 3 h and ca. 40%, 5 h)	-

UV: ultraviolet; MO: methyl orange.

Conclusions

Lac-TiO₂ was successfully prepared via an impregnation method. Different laccaic acid concentrations were studied. The properties of Lac-TiO₂ photocatalysts were examined through XRD, FE-SEM, XPS, DRS, FTIR, nitrogen adsorption/desorption, and PL spectroscopy. The TiO₂ phases found in the as-prepared pure TiO₂ and Lac-TiO₂ samples were mixtures of anatase and amorphous phases. FE-SEM images revealed that the synthesized TiO₂ samples were highly agglomerated into nearly spherical-like structure. XPS data showed the presence of Ti, O, C elements in the Lac-TiO₂. DRS results revealed an increase in the visible light absorption in the Lac-TiO₂ samples compared to that of the pure TiO₂ sample. The characteristic vibrational bands of Lac-TiO₂ were confirmed by FTIR technique. In addition, the 1.0Lac-TiO₂ sample has a higher specific surface area than pure TiO₂ providing more active sites. The photocatalytic performance of the Lac-TiO₂ samples was higher than that of the pure TiO₂ sample because it could generate a higher concentration of hydroxyl radicals under visible light irradiation. Our work showed that laccaic acid potentially enhanced the photocatalytic activity of TiO₂ under visible light.

Acknowledgments

This research is financially supported by Silpakorn University (Fiscal Year 2018).

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Edited by

Editor handled this article: Jaísa Fernandes Soares

Publication Dates

• Publication in this collection
  30 May 2022
• Date of issue
  2022

History

• Received
  12 Aug 2021
• Published
  07 Jan 2022