Synthesis and Characterization of Iodine-Doped TiO₂ Photocatalyst with Advanced Photocatalytic Degradation of Toxic Methyl Orange and Congo Red

Abstract

Iodine-based titanium dioxide composite (I-TiO₂) was prepared by following the trouble-free hydrolysis method using iodic acid and tetrabutyl titanate. The prepared TiO₂ and I-TiO₂ composites have been characterized by XRD, SEM, UV-visible spectroscopy, EDS, and FTIR spectroscopy. The anatase TiO₂ was confirmed by XRD diffraction patterns with 5.699 nm in size. The successful synthesis of TiO₂ both pure and doped was studied by FTIR spectroscopy. The photocatalytic activity of the prepared materials was investigated for degradation of organic dyes such as methyl orange (MO) and congo red (CR) with the irradiation of visible and ultraviolet (UV) light. The efficacy of the degradation of MO using I-TiO₂ (15%) was 6.75 and 36.89 times greater than that using pure TiO₂ with the irradiation of UV and visible light, respectively. Similarly, I-TiO₂ (15%) showed superior photocatalytic activity to degrade CR compared to bare TiO₂ by irradiation with both visible and UV light. The largest degradation (99% under UV and 89% under visible light) of the MO was obtained using I-TiO₂ (15%) as catalyst after 210 minutes. The reuse of I-TiO₂ (15%) as catalyst was also investigated showing negligible reduction of photocatalytic efficiency.

Key words

photocatalyst - iodine-doped - TiO₂ - degradation - catalytic activity

Rapid industrialization results in the increase of wastewater containing many industrial pollutants, including textile organic compounds such as dyes, oils, detergents, cosmetics, inks, etc. Besides others, textile pollutants exert intense ecological, health, and aquatic problems since the biodegradation of these pollutants is quite slow. Moreover, dyes have mutagenic and carcinogenic effects. The separation and degradation of organic pollutants is vital to ensure a nontoxic and pollution free environment.[1] Previously, ozonation, reverse osmosis, filtration, adsorption, coagulation, etc., several conventional methods have been used for wastewater treatment.[2] [3] However, due to less efficient, long operating time, high cost, pH sensitivity, production of hazardous byproducts, environment vulnerability, etc., it is essential to search new methods to mitigate these problems.[3,4] Currently, the degradation of organic materials through advanced oxidation has been reported using semiconductor metal oxide nanomaterials, which increases the generation of hydroxyl radical (^•OH) in presence of UV and visible light.[3] ^, [5] [6] [7] Heterogeneous photocatalysis with metal oxide nanomaterials has gained attention for the removal of toxic materials from wastes under sunlight.[8] Undoubtably, titanium dioxide (TiO₂) is one of the most used and more effective nano photocatalyst for wastewater treatment, because of its unique properties such as availability, chemical stability, nontoxicity, low cost, good catalytic activity in presence of light at very low concentration, and so on[9] [10] Moreover, the excellent physicochemical properties of TiO₂, ecofriendly nature, and its ability to generate innumerable electrons maintaining its stability under light have made TiO₂ a propitious material for numerous applications.[11] [12] Besides all its advantageous properties, TiO₂ has few limitations as a catalyst because of its low charge separation efficiency (band gap –3.2 eV),[13] and/or it might be toxic for living organisms.[6] [14] Hence it is essential to improve the catalytical activity of TiO₂. Several strategies have been reported to increase the photocatalytic activity of TiO₂, such as adding/doping metals, other semiconductor-based nanomaterials and using hole scavengers. Doping is one of the superior optimistic strategies that can alter the conduction band (CB) and/or valence band (VB) of TiO₂, and improve the light absorption possessions.[15] However, doping of non-metal with TiO₂ showed better photocatalytic activities rather than metal-doped TiO₂ due to strong absorption peak with a red shift for non-metal-doped TiO₂ under the visible light range.[16] [17] [18] [19] Several non-metal dopants, for example carbon, nitrogen, phosphorus, iodine, fluorine, boron, sulfur, and so on, are popular to increase catalytic activity of TiO₂.[12] [20] [21] Iodine-modified TiO₂ shows a significant photocatalytic activity in the visible light region. The reduced band gap for TiO₂ is accountable to lessen the recombination of photogenerated electrons and holes.[22] The degradation of several types of dyes using different non-metal-doped TiO₂ have been previously reported in the literature.[3] [23] However, the photocatalytic activity of I-TiO₂ has been rarely described for the degradation of several textile dyes like congo red, methyl orange, nitrophenol, triethanolamine, glycerol monostearate, 2Na-EDTA, methyl paraben, propyl paraben, and others.

In this work, the synthesis of crystalline I-TiO₂ by the sol-gel method (the most versatile and common technique) at room temperature has been described. The catalytic activities of the I-TiO₂ were examined for oxidative degradation of congo red and methyl orange in presence of UV and visible light.

X-ray Diffraction (XRD) Analysis

XRD investigation was accomplished to assess phases, size, degree of crystallinity, chemical composition as well as crystal structure of nanomaterials. Figure [1] displays the XRD patterns of synthesized nanomaterials of TiO₂ and I-TiO₂, which all were calcined at 450 °C. XRD patterns show the almost similar sharp peaks of the pure tetragonal anatase phase of TiO₂ that demonstrates the purity of the synthesized samples. The diffraction peaks appeared at 2θ diffraction angle 25.47°, 36.93°, 38.00°, 48.02°, 54.44°, 62.62°, 69.49°, and 75.20° for the lattice planes (101), (103), (004), (200), (105), (204), (116), and (215), respectively.[24] There are no characteristic peaks observed in the XRD patterns related to rutile, brookite, iodine, or any other impurities in the samples. The average crystallite sizes of TiO₂ and I-TiO₂ were calculated from the most intense anatase peak (101) with the help of Debye–Scherrer’s equation (Equation 1).

Equation 1

Where D is the average size of the nanomaterials, k denotes the constant with the value 0.94, λ represents the wavelength of the X-ray radiation of Cu-Kα (λ = 1.5406 Å) and β denotes the full width at half maximum, and θ is Bragg’s diffraction angle.[25] The crystallite size was found to be 6.76, 6.96, 7.35, 6.35, 5.70 nm for bare TiO₂, I-TiO₂ (2%), I-TiO₂ (10%), I-TiO₂ (15%), and I-TiO₂ (20%)_, respectively. The crystallite size decreases with increasing of I into the TiO₂ matrix. Similar results were found in previous work.[26]

Figure 1 XRD patterns for TiO₂ and I-TiO₂ nanomaterials

FESEM Analysis

The morphology of surface and microstructure of both synthesized TiO₂ and I-TiO₂ were thoroughly examined by FESEM analysis. In Figure [2], the FESEM images depict distinct characteristics of these nanomaterials. Notably, Figure [2](a) illustrates that particles exhibit a more pronounced agglomeration in the case of pure TiO₂ in comparison to I-TiO₂ nanomaterials, as evident in Figure [2](b). The introduction of iodine into the TiO₂ matrix contributes to reduction in agglomeration, reaching its minimum at 10% I doping, followed by a slight increase at 15% I doping. All FESEM images of the synthesized bare TiO₂ and I-TiO₂ nanomaterials reveal a spherical shape. However, it is crucial to note that in the sol-gel chemical synthesis method, the microstructure, surface morphology, and crystalline structure of both TiO₂ and I-TiO₂ are influenced by various parameters such as the precursor, reaction temperature, and pH value.[27]

Figure 2 SEM image of (a) TiO₂, (b) I-TiO₂ (10%), and (c) I-TiO₂ (15%) with magnification of 50,000× and (d) I-TiO₂ (10%) with magnification of 100,000×

EDS Analysis

Figure [3] displays the EDS results for I-TiO₂ (15%) nanoparticles. The EDS spectrum of I-TiO₂ reveals sharp peaks corresponding to the elements titanium (Ti), oxygen (O), and iodine (I). Specifically, the highest peak at 0.525 KeV (energy) confirms the presence of oxygen (O), the peak at 4.508 KeV (energy) signifies titanium (Ti), and the peak at 3.936 KeV (energy) validates the existence of iodine (I). The spectrum unequivocally demonstrates the incorporation of iodine into the TiO₂ structure, substantiating successful deposition of iodine atoms on TiO₂. Moreover, it exhibits higher percentage of iodine in I-TiO₂ (15%) compared to that of I-TiO₂ (10%), (Table S1 in the Supporting Information).

Figure 3 EDS spectrum of I-TiO₂ (15%)

FTIR Spectral Analysis

FTIR analysis is employed to find out chemical characterization of numerous functional groups on the surface of synthesized nanomaterials. The FTIR spectra presented in Figure [4] depicts TiO₂ and I-TiO₂ with varying amounts of iodine, all calcined at 400 °C. The pronounced peak observed around 1623.5 cm^–1 is attributed to the presence of hydroxyl groups from water absorbed on the catalyst’s surface.[28] The peak at 3407.25 cm^–1 evidences the presence of Ti–OH bonds and hydrogen-bonded water species. The decreasing intensity of the peak for iodine indicates the smaller part of iodine in the composite materials of I-TiO₂ (Figure [4]). These findings contrast with previously reported results in iodine-doped composites.[6] [29] Consequently, it can be explained that iodine as hydrophobic repels water molecules and deposits on the surface of TiO₂. The broader peaks at 3139.8 cm^–1 and small peaks at 1395.34 cm^–1 correspond to H–I–H stretching and bending vibrations of hydroxyl groups absorbed on the catalyst’s surface.[30]

In the FTIR spectrum, sharp peaks at 442.6 and 849.5 cm^–1 attributed the lattice vibrations of anatase O–Ti–O bonding in TiO₂.[12] Additionally, the peak at 2343 cm^–1 indicates the presence of asymmetric stretching of CO₂ molecules.[31] Notably, this peak is slightly stronger in the undoped sample compared to the doped sample, as CO₂ formed adducts with I^– ions on the surface of I-TiO₂ composites.

Figure 4 FT-IR spectra of TiO₂ and I-(2–20%) TiO₂ nanomaterials

UV-Visible Absorption Spectral Analysis

Figure [5] shows the UV-visible absorption spectra for the prepared TiO₂ and I-TiO₂ materials. The optical absorption spectra for I-TiO₂ exhibits a stronger absorption edge in the 250–380 nm range compared to pure TiO₂ confirms the insertion of iodine in composite materials.[32]

Figure 5 UV-vis absorption spectra for TiO₂ and I-TiO₂

The decreasing band gap energy with increasing concentration of iodine in I-TiO₂ composites was confirmed by the red shift in the absorption edge. Furthermore, the optical activity of I-TiO₂ increases in the visible range with increasing iodine dopant.[33] [34]

The band gap (E_g ) was calculated using Tauc’s relation (Equation 2).

Equation 2

Here, α is the absorption coefficient, A represents a constant, and n = 1/2 for direct or n = 2 for indirect allowed transitions of semiconductors.[35] The value of the optical band gap (E_g ) has been calculated by extrapolating the linear region to α = 0 from the plotting (αhν)² against hν (Figure [6]). The calculated band gap of modified composite materials was found to be 2.277, 2.448, 2.634, 2.686, and 3.312 eV for I-TiO₂ (2%), I-TiO₂ (20%), I-TiO₂ (15%), I-TiO₂ (10%), and pure TiO₂, respectively. The band gap of all I-TiO₂ composites is significantly reduced compared to pure TiO₂. The band gap gradually decreased with increasing amount of iodine doping from I-TiO₂ (10%) to I-TiO₂ (20%). However, I-TiO₂ (2%) showed minimum band gap. The reduction of band gap and modification of light absorption ability of I-TiO₂ compared to pure TiO₂ indicates the synergic interaction between TiO₂ and doped iodine in I-TiO₂.

Figure 6 Tauc plot of pure TiO₂ and I-TiO₂ (2–15%) photocatalysts

Photocatalytic Activity

The photocatalytic activity of prepared pure TiO₂ and all I-TiO₂ composite materials was inspected to degrade 100 mL of 10 ppm MO using 100 mg of photocatalyst under the irradiation of both UV and visible light. Figure [7a] shows the photocatalytic degradation of MO using different photocatalysts under the irradiation of UV light. The photolysis reaction of MO with UV light was also monitored. As shown in Figure [7a] the MO was not degraded without photocatalyst with the irradiation of only UV light. The MO was stable at UV photolysis reaction. It was also observed that only small amounts of dye are adsorbed during the reaction using different catalysts. The 15% I-TiO₂ shows maximum photocatalytic activity.

Figure 7 (a) Photocatalytic degradation of MO using pure TiO₂ and different I-TiO₂ catalysts with the irradiation of UV light and (b) the corresponding plot of –ln(C/C ₀) versus irradiation time

The kinetics and reaction rate of the photocatalytic degradation process has been studied according to the Langmuir–Hinshelwood (L–H) model, which was developed by Turchi and Ollis. The model is expressed as Equation 3.[36] [37]

Equation 3

Where r ₀ is the degradation rate on the reaction, k is the rate constant, and K and C are the adsorption equilibrium constant and reactant concentration, respectively. If the initial concentration C ₀ is very small, it can be simplified to Equation 4.[36] [37]

Equation 4

The equation becomes a linear expression on time t with respect to –ln(C/C ₀), where k _obs is reaction rate constant. The values of k _obs were calculated by plotting –ln(C/C ₀) versus t (Figure [7b]). As shown in Table [1], it was observed that the degradation rate of MO by I-TiO₂ (15%) with the UV light irradiation (1.114 h^–1) was 6.75 times higher than that attained by pure TiO₂ (0.165 h^–1).

Table 1 Kinetic Parameters for Photocatalytic Degradation of MO under Irradiation of UV Light

Photocatalyst	Rate constant (h–1)	t 1/2 (h)	R2
pure TiO2	0.165	4.20	0.96
I-TiO2 (2%)	0.285	2.43	0.99
I-TiO2 (10%)	1.098	0.63	0.99
I-TiO2 (15%)	1.114	0.62	0.99
I-TiO2 (20%)	0.264	2.63	0.99

The photocatalytic degradation of MO using different photocatalysts with the irradiation of visible light was also investigated. As shown in Figure [8a], it was observed that I-TiO₂ (15%) showed maximum photocatalytic activity. The pseudo first order reaction rate constant of MO degradation using I-TiO₂ (15%) under the visible light irradiation (0.664 h^–1) is 36.89 times higher than that attained using pure TiO₂ (0.018 h^–1) (Figure [8b] and Table [2]).

Table 2 Kinetic Parameters for Photocatalytic Degradation of MO under Irradiation of Visible Light

Photocatalyst	Rate constant (h–1)	t 1/2 (h)	R2
pure TiO2	0.018	38.50	0.93
I-TiO2 (2%)	0.219	3.16	0.99
I-TiO2 (10%)	0.204	3.40	0.97
I-TiO2 (15%)	0.664	1.04	0.99
I-TiO2 (20%)	0.191	3.63	0.99

Figure 8 (a) Photocatalytic degradation of MO using pure TiO₂ and different I-TiO₂ catalysts irradiated by visible light and (b) the corresponding plot of –ln(C/C ₀) versus irradiation time

I-TiO2 (15%) showed maximum photocatalytic MO degradation activity even though it has a higher band gap compared to the band gap of I-TiO₂ (2%) and I-TiO₂ (20%). The slower photogenerated electron-hole pair recombination rate and higher charge transfer of I-TiO₂ (15%) would be responsible for its enhanced photocatalytic activity. However, excess iodine in the I-TiO₂ (20%) may function as electron–hole pair recombination centers and decrease photoinduced charge separation.[38] [39]

The photocatalytic degradation ability of I-TiO₂ (15%) to degrade another textile dye CR was also compared with the pure TiO₂ under UV and visible light irradiation. As shown in Figure [9] and Table [3], the pseudo first order reaction rate constant of MO degradation using I-TiO₂ (15%) under UV light irradiation (0.595 h^–1) is 1.82 times higher than that attained using pure TiO₂ (0.327 h^–1). On the other hand, the rate constant using I-TiO₂ (15%) under the visible light irradiation (0.325 h^–1) was about 36 times better than that attained using pure TiO₂ (0.009 h^–1) (Figure [10] and Table [3]).

Figure 9 (a) Photocatalytic degradation of CR using pure TiO₂ and I-TiO₂ (15%) catalysts with the irradiation of UV light and (b) the corresponding plot of –ln(C/C₀) versus irradiation time

Figure 10 (a) Photocatalytic degradation of CR using pure TiO₂ and I-TiO₂ (15%) catalysts with the irradiation of visible light and (b) the corresponding plot of –ln(C/C ₀) versus irradiation time

Table 3 Kinetic Parameters for Photocatalytic Degradation of CR

Photocatalyst	Type of irradiated light	Rate constant (h–1)	t 1/2 (h)	R2
pure TiO2	UV	0.327	2.12	0.99
I-TiO2 (15%)	UV	0.595	1.16	0.98
pure TiO2	visible	0.009	77.00	0.95
I-TiO2 (15%)	visible	0.325	2.13	0.97

In order to inspect the influence of pH on the photocatalytic degradation of textile dye using I-TiO₂ (15%), the photocatalytic degradation of CR was performed at different pH using 15% I-TiO₂ under visible light irradiation.

It has been shown that 15% I-TiO₂ showed higher dye removal efficiency at near neutral pH (pH 6) (Figure [11]). A massive decline was seen when pH of the solution changes to basic or acidic. Similar results were reported in previous works.[5] [30] The lowering of dye removal efficiency for TiO₂ indicates the agglomeration of TiO₂ in acidic conditions, which may cause a reduction of the available surface area for dye adsorption and photon absorption. Moreover, at higher pH, the rate of degradation decreases. The catalyst surface gets negatively charged and limiting photocatalytic degradation.[5] It has been reported that at higher pH values, OH^– react with photogenerated h⁺ and form ^•OH resulting the reduction of degradation efficiency.[40]

Figure 11 Effect of pH on the rate of the degradation of CR using 15% I-TiO₂ under visible light irradiation

Stability and Reusability of Catalysts

The recyclability or reusability of catalyst is very important feature to determine the stability of catalyst in practical applications.[5] The reusability as well as stability of the I-TiO₂ (15%) photocatalyst on the degradation of MO under UV light irradiation was studied. The catalyst was separated by centrifugation and reused for further degradation of CR at same condition. The catalytic efficiency of each cycle was calculated using Equation 5.

Equation 5

Where A ₀ is the absorbance of MO dye at initial time and A _t is the absorbance of MO dye after 3.5 hours of UV irradiation in each cycle.

It was found that the catalyst is very stable for up to three cycles and degradation ability decreased by small amount after three cycles (Figure [12]). The possible explanation for a small decrease in photocatalytic activity is the chemisorption of CR molecules or reaction intermediate products on the active sites of the catalyst, which remain after the saturation of accessible sites for further reactions. The results indicate that the I-TiO₂ (15%) photocatalyst can be reused on the photocatalytic degradation study.

Figure 12 Reusability of I-TiO₂ (15%) in the photocatalytic degradation of MO under UV light irradiation

Evaluation of the Mineralization of Real Water Sample by Chemical Oxygen Demand (COD) Studies

Chemical oxygen demand (COD) values for untreated textile effluent solutions and treated textile effluent solutions using different catalysts under the same reaction conditions were calculated. The percentage decline of COD values using different catalysts was calculated using Equation 6.

Equation 6

As shown in Table [4], it was observed that the COD decrement rate of I-TiO₂ increased with increasing doped amount of iodine with maximum COD decrement observed for I-TiO₂ (15%). However, the COD decrement rate slightly decreased with when doping increased to I-TiO₂ (20%).

Table 4 Decrement Rate for COD Values of Textile Effluent Using TiO₂ and Different I-TiO₂ composite materials.

Photocatalyst	COD removal efficacy (%)
pure TiO2	29.25
I-TiO2 (2%)	31.13
I-TiO2 (10%)	66.98
I-TiO2 (15%)	79.25
I-TiO2 (20%)	62.26

Proposed Mechanism

On the basis of literature, superoxide, hydroxyl radical and holes are participated in the photocatalytic degradation of dyes.[5] ^, [41] [42] [43] The possible mechanism for the degradation of dyes using I-TiO₂ under the irradiation of light is shown Figure [13].

Figure 13 Proposed mechanism of photocatalytic degradation of CR/MO using I-TiO₂

In brief, under light irradiation, electrons and holes are generated in the conduction band and valence band of the I-TiO₂. Iodine may take part in slower the recombination of photogenerated electrons and holes. Hence, photogenerated electrons and holes reacted with environmental oxygen and water to produce superoxide (O₂ ^•–) and hydroxyl (^•OH) radicals, respectively. After that, the superoxide, hydroxyl, and photogenerated holes react with dye solution to produce degradation products. The steps involved in the mechanism of photocatalytic degradation of dyes using I-TiO₂ are shown below and in Figure [13]

I-TiO₂ + hν → I-TiO₂ (e^– + h⁺)

I-TiO₂ (h⁺) + H₂O → I-TiO₂ + H⁺ + ^•OH

I-TiO₂ (h⁺) + OH^– → I-TiO₂ + ^•OH

I-TiO₂ (e^–) + O₂ → I-TiO₂ + O₂ ^•–

dyes + ^•OH/O₂ ^•–/h⁺ → degraded products

Conclusions

The prepared I-TiO₂ composite materials were formed using the simple sol-gel method at room temperature. The crystallinity and the morphology of the prepared I-TiO₂ samples was analyzed using XRD and SEM. UV-visible measurements showed the tuning of the optical band gap of I-TiO₂ with significant reduction in the optical band gap of I-TiO₂ composites compared to pure TiO₂. I-TiO₂ (15%) showed better catalytic activity for the degradation reaction of the aforementioned dyes, MO, and CR. The reusability test indicated the I-TiO₂ (15%) was photostable for three catalytic cycles. The presence of iodine in the prepared different I-TiO₂ composite materials is responsible for the advancement of the catalytic activity for the degradation reaction.

Materials and Methods

Tetrabutyl titanate (C₁₆H₃₆O₄Ti), iodic acid (HIO₃), and EtOH were purchased from Sigma Aldrich. HNO₃, NaOH, congo red, and methyl orange were obtained from Merck, Germany. These chemicals and reagents are of analytical grade of purity and used without further treatment.

Synthesis of Pure and I-Doped TiO₂

I-TiO₂ were prepared by following a very simple schematic hydrolysis method where tetrabutyl titanate (TBOT) and iodic acid were used as precursors.[28] The two solutions were prepared, one containing TBOT and another containing various portions of iodic acid. A mixture of EtOH and HNO₃ was used as a solvent to dissolve TBOT. Double distilled water was used to dissolve iodic acid for preparation of different I-TiO₂ composites with various amounts of iodine to TiO₂ (2–20%). Both the solution of HIO₃ and TBOT were mixed properly over a mechanical stirrer (stirring rate 950 rpm, 8 h). The resultant mixture was dried (100 °C), ground, and calcined (400 °C, 2 h). Pure TiO₂ was prepared following the same procedure without using any iodic acid solution.

Photocatalytic Activity Measurement Under UV Light

The UV photoreactor equipped with an open Pyrex glass tube and a thermosetting jacket (maintaining 25 °C), three fluorescent lamps (Vilber-Lourmat T-6L UV-A, 6 W, λ _max = 365 nm) was used for photocatalysis under UV light. Photocatalyst (100 mg) was used to degrade the dye solution (100 mL). The reaction mixture was kept in the dark for 30 min to ensure the adsorption–desorption equilibrium before illumination under UV light irradiation. The irradiation time varied from 2 to 5 h. Aliquot portions (4 mL) of the suspensions were collected every 30 min and photocatalyst was removed by centrifugation (Eppendorf Centrifuge 5810R, 4000 rpm, for 5 min).

Photocatalytic Activity Measurement Under Visible Light

Tungsten halogen lamp (200 W), filter made up of glass, quartz cylinder and fan (for cooling) were used to assemble a photoreactor for photocatalysis in presence of visible light (λ_max < 420 nm). Photocatalyst (100 mg) was used to degrade dye solution (100 mL). The investigation was carried out at ambient temperature. The sample was kept 20 cm away from the lamp on magnetic stirrer. To establish absorption–desorption equilibrium the reaction mixture was kept in the dark before light irradiation at room temperature. At regular intervals (30 min), portions of the reaction mixture (4 mL) were taken out and centrifuged to remove the photocatalyst.

Regeneration of Used Photocatalyst

The prepared I-TiO₂ (15%) composites were reused four times as catalyst for the degradation of aforementioned dyes. To separate the catalyst the reaction mixture was centrifuged (20 min, 3000 rpm) and washed using double distilled water. The separated catalyst was dried (100 °C) and calcined (400 °C, 2 h) in a crucible.

Chemical Oxygen Demand (COD) Test

In order to evaluate the mineralization ability of pure TiO₂ and iodine-doped TiO₂ composites, an industrial effluent containing CR and MO dyes was treated with the photocatalyst in presence of visible light for up to 6 h. Then the COD of the untreated and treated industrial effluents was calculated using the standard FAS method. Briefly, the sample was refluxed with K₂Cr₂O₇ (10 mL, 0.25 M) and H₂SO₄ (30 mL, 2 M). (NH₄)₂Fe(SO₄)₂·6H₂O (0.25 M) was used to titrate the remaining dichromate in the sample after reflux.[44]

Characterization Techniques

Field Emission Scanning Electron Microscope (JSM-7600F, JEOL) was employed to investigate the surface morphology and microstructure of the fabricated samples. SEM images of different magnification were taken by maintaining an accelerating voltage of 5 kV and current of 10 μA. Functional groups as well as successful formation of bare TiO₂ and doped TiO₂ were investigated at room temperature by FTIR analysis (IRTracer, Shimadzu, Japan). The recorded FTIR spectra with average scan of 40 in the range of wavenumber 400–4000 cm^–1 of synthesized samples were performed using the KBr disk preparation method. In order to characterize the light absorption ability of the TiO₂ and doped TiO₂, the absorption spectra were recorded in the range of 200–800 nm wavelengths by UV-visible spectroscopy (UV-1800, Shimadzu, Japan). Moreover, photodegradation study was carried out by recording the absorption spectra of MB and CR dyes by UV-visible spectroscopy (UV-1800, Shimadzu, Japan). In order to investigate compositional and structural information about the synthesized nanomaterials XRD analysis were performed by Rigaku smartlab diffractometer using Cu-Kα radiation (λ = 1.5406 Å). The XRD patterns were recorded at room temperature over the 2θ angle range from 10 to 90 with scan rate of 0.02°. The average crystalline sizes of synthesized nanomaterials were calculated with the help of the Scherrer formula.

Conflict of Interest

All experiments were conducted at Department of Chemistry, Jagannath University. Any opinions, findings, conclusions, or recommendations expressed in this paper are those of the authors and do not necessarily reflect the view of the supporting organizations

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Publikationsverlauf

Eingereicht: 05. Oktober 2025

Angenommen nach Revision: 13. November 2025

Artikel online veröffentlicht:
15. Dezember 2025