Effects of Initial Nitrate Concentrations and Photocatalyst Dosages on Ammonium Ion in Synthetic Wastewater Treated by Photocatalytic Reduction

Rojviroon, Orawan; Sirivithayapakorn, Sanya; Rojviroon, Thammasak; Wantawin, Chalermraj

doi:https://doi.org/10.1155/2020/8893816

International Journal of Photoenergy

On this page

Abstract Introduction Materials Results and Discussion Conclusion Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Special Issue

New Environmentally Friendly Solar Energy and Hydrogen Storage Materials

View this Special Issue

Research Article | Open Access

Volume 2020 | Article ID 8893816 | https://doi.org/10.1155/2020/8893816

Effects of Initial Nitrate Concentrations and Photocatalyst Dosages on Ammonium Ion in Synthetic Wastewater Treated by Photocatalytic Reduction

Orawan Rojviroon,¹Sanya Sirivithayapakorn,¹Thammasak Rojviroon,²and Chalermraj Wantawin¹

Academic Editor: Jiangwei LIU

Received06 Aug 2020

Revised16 Oct 2020

Accepted24 Oct 2020

Published16 Nov 2020

Abstract

Ammonium () is an undesirable by-product of photocatalytic nitrate () reduction since it is harmful to aquatic life once it converts into ammonia (NH₃). This research investigated the removal efficiency of and for the first time quantified the relationships of initial nitrate concentrations ([]₀) and photocatalyst dosages on the remaining ammonium () in synthetic wastewater using photocatalytic reduction process with either nanoparticle titanium dioxide (TiO₂) or 1.0%Ag-TiO₂ under Ultraviolet A (UVA). The experiments were systematically carried out under various combinations of []₀ (10, 25, 50, 80, and 100 mg-N/L) and photocatalyst dosages (0.1, 0.5, 1.0, and 2.0 g). The removal efficiency of both photocatalysts was 98.96-99.98%, and the catalytic selectivity products were nitrogen gas (N₂), nitrite (), and . Of the two photocatalysts under comparable experimental conditions, 1.0%Ag-TiO₂ provided better removal efficiency. For both photocatalysts, the remaining was predominantly determined by []₀; higher []₀ led to higher . Multiple linear regression analysis confirmed the dominant role of []₀ in the remaining . The photocatalyst dosage could play an essential role in limiting in the treated wastewater, with large variation in []₀ from different sources.

1. Introduction

Photocatalytic reduction is an effective technology for removal of nitrate () in wastewater. The major disadvantage of this process is the ammonium (), an undesirable by-product, remaining at the end. Many researchers studied removal efficiency and the conversion selectivity [1–3]. There are also studies on the influencing factors on the remaining , which investigated the relationships between remaining and those influencing factors in the process.

Previous studies demonstrated that high efficiency nitrate removal by photocatalytic reduction with low remaining [] could be achieved by silver- (Ag-) doped TiO₂ nanoparticles under high-performance light sources (i.e., high-pressure Hg lamps and xenon lamps) [4–6]. However, those light sources have disadvantages that include high energy consumption, potential human health hazard, and generating high heat [7, 8]. For those reasons, the UVA light bulb is chosen for this process because it overcomes those disadvantages and is powerful enough for this process [9–11].

The influencing factors of the photocatalytic selectivity of conversion include initial nitrate concentration ([]₀), light source intensity, type of photocatalyst, type of dopant, and quantity of photocatalyst dosage [4, 12, 13]. Evidence shows that manipulating the photocatalytic selectivity of photocatalytic reduction helps limit environmentally harmful compounds, particularly [14, 15]. is harmful to aquatic life once in the natural waterways where it converts into ammonia (NH₃). According to the United States Environmental Protection Agency (US EPA), the upper safety limit of total ammonia nitrogen (NH₃-N) is 17 mg-N/L (1-hour average) and 1.9 mg-N/L (30-day rolling average) at pH 7.0 and 20°C for acute and chronic criteria, respectively [16]. The reported total ammonia concentrations in treated wastewater from photocatalytic reduction vary between 0.07 and 57.8 mg-N/L [4, 17–22].

Doping of silver (Ag⁺) on photocatalysts, especially TiO₂, to improve the photocatalytic performance was a common practice. Previous studies applied 0.1%-7.0% Ag⁺ loading on TiO₂ photocatalysts and found that 1% Ag⁺ was the most optimum dose to enhance the photocatalytic reduction activity [23–25].

This research investigated the effects of initial nitrate concentrations ([]₀) and photocatalyst dosages on removal efficiency in synthetic wastewater using photocatalytic reduction. The experiments were carried out under various []₀ (10, 25, 50, 80, and 100 mg-N/L) and photocatalyst dosages (0.1, 0.5, 1.0, and 2.0 g) under UVA irradiation as light source for photocatalytic nitrate reduction. The experimental photocatalysts were TiO₂ and 1.0%Ag-TiO₂ nanoparticle as photocatalysts [21]. The catalytic selectivity of conversion was also determined, and the actual concentrations of under different experimental removal conditions were compared. Multiple linear regression was performed to characterize the relationship between the remaining and []₀ and photocatalyst dosages. Essentially, the novelty of this research lies in the use of TiO₂ nanopowder as photocatalyst, as opposed to commercial-grade TiO₂. By comparison, TiO₂ nanopowder possesses larger surface area for adsorption and reaction. Another research novelty is the systematical use of various []₀ and photocatalyst dosages, unlike previous researches which experimented with specific []₀ and photocatalyst dosages.

2. Materials and Methodology

2.1. Ag-TiO₂ Photocatalyst Preparation and Characteristics

In this research, 1.0%Ag-TiO₂ photocatalyst was prepared by composite colloid deposition under alkaline condition, following Doudrick et al. [4, 9] with minor modifications. In the experiment, 12 g of TiO₂ nanopowder was dispersed in 500 mL deionized water and purged with nitrogen gas (N₂) for 30 min to remove O₂. After degassing, 8 mL of methanol was added and stirred prior to adding NaOH to adjust pH of the mixture to 12-13. Afterward, 1.0%AgNO₃ (; Fluka) was added and stirred in the dark for 30 min before irradiation with UVA (800 μW/cm²) for 1 h at room temperature.

The mixture was then centrifuged at 200 rpm for 2 min to settle the powder, and the supernatant was discarded. Deionized water was added to wash the powder. It was then stirred and centrifuged. The process was repeated until the mixture pH was 7. The washed powder was oven dried at 103°C for 24 h and calcined at 450°C for 1 h for Ag-TiO₂ photocatalyst in the form of dried light purple powder.

The experimental TiO₂ nanopowder was of 15 nm in particle size and 99.5% anatase crystalline phase (US Research Nanomaterials, Inc., USA). The composition and specific surface area of dose photocatalysts were characterized by transmission electron microscopy (TEM, JEM-1400 TEM instrument) and X-ray fluorescence spectrometer (XRF; Bruker model S8 Tiger), Brunauer, Emmett and Teller (BET) analyzer (BELSORP-max Bel Japan Inc.).

2.2. Photocatalytic Reduction for Removal

The photocatalytic reduction to remove nitrate () was carried out using TiO₂ and Ag-TiO₂ photocatalysts in 125 mL cylindrical borosilicate glass photoreactor. Figure 1 illustrates the schematic of experimental photocatalytic reduction for removal. Synthetic wastewater of variable initial nitrate concentrations was prepared by dissolving potassium nitrate (, Fluka) in deionized water. The initial nitrate concentration ([]₀) varied between 10, 25, 50, 80, and 100 mg-N/L.

The photoreactor was filled with 100 mL synthetic wastewater of varying []₀ and 58 mM of formic acid (FA) as hole scavenger, with the mixture pH ranging from 2.28 to 2.42. TiO₂ and Ag-TiO₂ photocatalysts of varying dosages were independently added into the photoreactor. The photocatalyst dosage was varied from 0.1, 0.5, 1.0, and 2.0 g. The photoreactor condition was anaerobic by purging with N₂ for 30 min to remove dissolved oxygen (DO) in the synthetic wastewater.

Prior to UVA irradiation, samples were drawn for initial measurement of pH, DO, [], [], and []. The samples were subsequently irradiated with two UVA light bulbs (300 W, Osram) for 6 h. The UVA light bulbs were located on either side of the photoreactor vessel at a distance of 20 cm. The UVA intensity in the photoreactor vessel was 800 μW/cm² on average. The concentrations of and by-products ([] and []) relative to reaction time were periodically measured throughout the experiment, while pH and DO were measured at the beginning and at termination (at 360 min). The concentrations of , , and in the synthesis wastewater were determined using ion chromatography instrument with chemical suppression (Metrohm 882 Compact IC Plus). Nitrogen gas (N₂) was calculated by the mass balance of nitrogen of the photocatalytic reduction process.

To verify the experiment, photocatalytic reduction was also carried out under three control conditions: (1) in the absence of photocatalyst but with UVA irradiation; (2) with Ag-TiO₂ photocatalyst of varying dosages but without UVA irradiation; and (3) with TiO₂ photocatalysts of varying dosages but without UVA irradiation. The measured [], [], and [] of photocatalytic reduction using Ag-TiO₂ and TiO₂ photocatalysts irradiated with UVA were subsequently compared against the controls.

2.3. Selectivity of Photocatalytic Reduction for Removal

The removal efficiency of photocatalytic reduction () and the catalytic selectivity () of into , , and N₂ (denoted by , , and ) [21, 26] are mathematically expressed in the following equations.

where is the initial concentration of and is the concentration of at time .

3. Results and Discussion

3.1. Ag-TiO₂ Nanopowder Photocatalyst Characteristics

The results of transmission electron microscopy were used to examine the particle size and morphology of Ag nanoparticles on TiO₂ as well as the lattice information of both photocatalysts investigated by XRF. In comparison, the TEM image of nano-TiO₂ and nano-Ag-TiO₂ photocatalysts (Figure 2) showed a similar particle size and morphology with average particle size (in diameter) of approximately 15 nm (as the result of the average TiO₂ particle size before Ag doping). The results of the TEM analysis were not clearly distinguishable in terms of particle size and morphology although it was reported that Ag doping would slightly decrease the particle size of the larger TiO₂ powders [27].

(a) TiO2

(b) Ag-TiO2

The XRF patterns of TiO₂ and 1.0%Ag-TiO₂ nanopowder photocatalysts showed strong peaks of Ti, as shown in Figure 3. The XRF pattern of 1.0%Ag-TiO₂ photocatalyst indicated that Ag⁺ dopant was effectively doped onto TiO₂ which is the same with the theoretical adding. The Ag dopant in Ag-TiO₂ phase was 0.99% for theoretical doping of 1.0% (Table 1). It was confirmed that Ag was effectively deposited on the surface of TiO₂ nanopowder. Specifically, Ag⁺ ions were adsorbed onto the crystal structure of TiO₂ and subsequently formed Ag-TiO₂ [28, 29].

The BET specific surface areas of TiO₂ and 1.0%Ag-TiO₂ nanopowder photocatalysts were and , and the corresponding pore volumes were and . It was found that the specific surface area and pore volume of Ag-TiO₂ were decreased after doping. The findings were consistent with previous studies which doped TiO₂ nanopowder photocatalysts with varying dopants [4, 30, 31].

The slightly decreased BET surface areas and pore volume were due to the interference of Ag dopant on the formation of anatase crystallization [32, 33], and a marked influence on the microstructures was exhibited by calcination temperature [34]. However, the advantage of metal doping on semiconductor particles, Ag-TiO₂, was the prevention of recombination between electron and hole by trapping the electron on the metal surface resulting in increasing the lifetime of electron in conduction band, thus enhancing the efficiency of photocatalytic nitrate reduction [34].

3.2. Removal Using Photocatalytic Reduction

The removal efficiency () of photocatalytic reduction using TiO₂ and 1.0%Ag-TiO₂ photocatalysts under variable initial concentrations ([]₀; 10, 25, 50, 80, and 100 mg-N/L) and TiO₂ and 1.0%Ag-TiO₂ dosages (0.1, 0.5, 1.0, and 2.0 g) was determined by equation (1).

Table 2 tabulates the removal efficiency, nitrate concentration at termination ([]_t), ammonium ion selectivity (), and actual ammonium ion concentration ([]_a) of photocatalytic reduction under various []₀ using TiO₂ and 1.0%Ag-TiO₂ photocatalysts. The removal efficiency of TiO₂ and 1.0%Ag-TiO₂ photocatalysts was 98.96-99.98%. The removal efficiency increased with the increase in photocatalyst dosage as the surface area for adsorption and reaction increased.

The ammonium ion selectivity () and actual ammonium ion concentration ([]_a) increased with the increase in photocatalyst dosage for both TiO₂ and 1.0% Ag-TiO₂ photocatalysts. In addition, the initial nitrate concentration and []_a were positively correlated. In other words, low []₀ resulted in low []_a and vice versa. Moreover, []_a of 1.0% Ag-TiO₂ photocatalyst was higher than that of TiO₂ photocatalyst under all experimental conditions.

The reduction in photocatalytic process was a stepwise mechanism. When the photoinduced electrons (e^-) in valence band were excited onto conduction band, holes (h⁺) appeared at valence band. This process was called electron-hole pairs photogeneration [32] (equation (5)). The photogenerated holes consumed HCOO^-, and was generated [35] (equation (6)). The is a strong reducing agent to reduce to either or N₂ (equations (7)–(12)), in which nitrite () was an intermediate product. The results of , , and N₂ in percent named the selectivity of reduction.

In the nitrate reduction experiments, 58 mmol of formic acid (FA) was used as a hole scavenger to improve the photocatalytic reduction reaction, while the pH of the solution increased from 2.28-2.42 to 2.41-5.5 due to the consumption of formic acid in the reaction and the generation of []. In addition, the highly efficient conversion of to N₂ was also related to the initial acidity of the solution [36]. This was probably due to the specific absorption properties of and in varying pH solutions. Considering that the point of zero charge of the TiO₂ was 6.25 [37], in acidic solution, TiO₂ surface accumulated a net positive charge due to the increasing fraction of TiOH₂⁺ sites on the surface and could be quickly adsorbed.

Figure 4 compares the nitrate concentrations of photocatalytic reduction under various []₀ and photocatalytic dosages (TiO₂ and 1.0%Ag-TiO₂) from the start to end. In Figure 4, the removal was positively correlated with photocatalyst dosage due to the surface area effect, independent of photocatalyst type. Although at termination there were not much differences in final removal efficiencies, the removal rates of 1.0%Ag-TiO₂ photocatalyst were faster than those of TiO₂ photocatalyst for the comparable conditions. The faster removal rate of photocatalytic reduction activity was attributable to Ag⁺ doping [33, 38]. The loading of TiO₂ with Ag⁺ reduced the difference between energy levels of the valence and conduction bands, resulting in the extension of light absorption wavelength into the visible light region. Ag⁺ also acted as a trap site for excited electrons, giving rise to electron-hole separation. In addition, Ag⁺ doping enhanced charge transport, prolonged the lifetime of electron-hole pairs, and reduced the charge recombination [39–42]. As a result, Ag⁺ could be adopted for photocatalytic reduction process to improve removal.

Figure 5 illustrates the catalytic selectivity (%) of photocatalytic reduction using TiO₂ and 1.0%Ag-TiO₂ photocatalysts in which was transformed into , , and N₂. The results showed that overall N₂ accounted for the largest proportions of by-products, followed by and .

In Figure 5, the photocatalyst types (TiO₂ and 1.0%Ag-TiO₂) and dosage played a role in the selectivity of the photocatalytic reduction scheme. This showed that the Ag dopant enhanced the photocatalytic reduction activity, and both the activity and [] increased with 1.0%Ag-TiO₂ dosage increase. However, 1.0%Ag-TiO₂ photocatalyst dosage beyond 0.1 g (i.e., 0.5, 1.0, and 2.0 g) contributed to [] in the treated wastewater exceeding that of TiO₂ photocatalyst (Table 2). is harmful to aquatic life once in the natural waterways where it converts into NH₃.

The initial nitrate concentrations also played a role in [] in the treated wastewater, independent of photocatalyst type (TiO₂ and 1.0%Ag-TiO₂). Specifically, higher []₀ resulted in higher []. Given 0.1 g of either TiO₂ or 1.0%Ag-TiO₂ photocatalyst, [] was 1.96-16.09 mg-N/L, independent of []₀. Assuming complete -to-NH₃ conversion, these were equivalent to 1.96-16.09 mg-N/L total ammonia nitrogen (NH₃-N), which is below 17 mg-N/L NH₃-N of the US EPA [16]. Meanwhile, the nitrate concentrations of the three control conditions (i.e., the controls) remained unchanged at the end of the experiment.

In Figure 5, the catalytic selectivity of into could also be observed. The remaining nitrite concentrations ([]) were negligible as was converted into and N₂ during the photocatalytic reduction process [43].

To comparatively investigate the effect of initial nitrate concentration and photocatalyst dosage on the concentration of ammonium ion, the relationships between [] and []₀ and photocatalyst dosage (TiO₂ and 1.0%Ag-TiO₂) were established by using statistical multiple linear regression. [], []₀, and photocatalyst dosage are denoted by , , and , respectively. The multiple linear regression was expressed in equation (13), and Table 3 tabulates the regression results. where is the linear regression constant, is the linear regression coefficient, and is the error constant.

In Table 3, of the initial nitrate concentration ([]₀) was, respectively, 0.925 and 0.838 for TiO₂ and 1.0%Ag-TiO₂ photocatalysts (), indicating that []₀ played the dominant role in removal efficiency and the remaining . Meanwhile, of photocatalyst dosage was 0.407 and 0.288 for 1.0%Ag-TiO₂ and TiO₂ photocatalysts, suggesting that the photocatalyst dosage had considerably less effect on the remaining .

In reality, []₀ varies from area to area. Given diverse []₀, it is operationally practical to vary the photocatalyst dosage in the photocatalytic reduction scheme. Based on the experimental results, 0.1 g of Ag-TiO₂ photocatalyst is advisable due to efficient removal of (Figure 3).

To facilitate estimation of the remaining [] in treated wastewater using photocatalytic reduction, the multiregression prediction equations of the theoretical remaining ammonium ion ([]_T), as a function of []₀ and photocatalyst dosage, are expressed in equations (14) and (15), respectively.

The prediction equation for TiO₂ photocatalyst is

The prediction equation for 1.0%Ag-TiO₂ photocatalyst is

The relationships between []_T, [], and photocatalyst dosage, as shown in equations (7) and (8), could be further applied to estimate the remaining [] under various []₀ and photocatalyst dosages.

4. Conclusion

This research investigated the removal efficiency of photocatalytic reduction process under various []₀ (10, 25, 50, 80, and 100 mg-N/L) and photocatalyst dosages (0.1, 0.5, 1.0, and 2.0 g) using nanoparticle TiO₂ and 1.0%Ag-TiO₂ photocatalysts under UVA. The removal efficiency of both photocatalysts under experimental []₀ and photocatalyst dosages was between 98.96 and 99.98%. The catalytic selectivity products were , , and N₂, with N₂ accounting for a significant proportion of the selectivity. The doping of TiO₂ with Ag⁺ improved the removal efficiency of . It was found that []₀ played a more important role in the remaining than the photocatalyst dosage. Specifically, higher []₀ led to higher [] in the treated wastewater. Multiple linear regression analysis confirmed the dominant role of []₀ in the remaining .

Data Availability

The analysis data used to support the findings of this study are included within the supplementary information file(s).

Conflicts of Interest

The author(s) declare(s) that they have no conflicts of interest.

Acknowledgments

The authors would like to express sincere gratitude to the Faculty of Engineering, Kasetsart University, Thailand, for the technical support.

References

N. Tong, Y. Wang, Y. Liu et al., “PdSn/NiO/NaTaO3:La for photocatalytic ammonia synthesis by reduction of NO3− with formic acid in aqueous solution,” Journal of Catalysis, vol. 361, pp. 303–312, 2018.
View at: Publisher Site | Google Scholar
Y. A. Shaban, A. A. El Maradny, and R. K. Al Farawati, “Photocatalytic reduction of nitrate in seawater using C/TiO₂ nanoparticles,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 328, pp. 114–121, 2016.
View at: Publisher Site | Google Scholar
D. Sun, W. Yang, L. Zhou, W. Sun, Q. Li, and J. K. Shang, “The selective deposition of silver nanoparticles onto {1 0 1} facets of _{TiO 2} nanocrystals with co-exposed {0 0 1}/{1 0 1} facets, and their enhanced photocatalytic reduction of aqueous nitrate under simulated solar illumination,” Applied Catalysis B: Environmental, vol. 182, pp. 85–93, 2016.
View at: Publisher Site | Google Scholar
K. Doudrick, T. Yang, K. Hristovski, and P. Westerhoff, “Photocatalytic nitrate reduction in water: managing the hole scavenger and reaction by-product selectivity,” Applied Catalysis B: Environmental, vol. 136-137, pp. 40–47, 2013.
View at: Publisher Site | Google Scholar
R. Lucchetti, L. Onotri, L. Clarizia et al., “Removal of nitrate and simultaneous hydrogen generation through photocatalytic reforming of glycerol over “in situ” prepared zero-valent nano copper/P25,” Applied Catalysis B: Environmental, vol. 202, pp. 539–549, 2017.
View at: Google Scholar
E. Bahadori, A. Tripodi, G. Ramis, and I. Rossetti, “Semi-batch photocatalytic reduction of nitrates: role of process conditions and co-catalysts,” ChemCatChem, vol. 11, no. 18, pp. 4642–4652, 2019.
View at: Publisher Site | Google Scholar
Z. W. Lipsky and G. K. German, “Ultraviolet light degrades the mechanical and structural properties of human stratum corneum,” Journal of the Mechanical Behavior of Biomedical Materials, vol. 100, article 103391, 2019.
View at: Publisher Site | Google Scholar
T. F. Anderson, “Artificial light sources,” Dermatologic Clinics, vol. 4, no. 2, pp. 203–215, 1986.
View at: Publisher Site | Google Scholar
T. Rojviroon and S. Sirivithayapakorn, “E. coliBacteriostatic action using TiO2Photocatalytic reactions,” International Journal of Photoenergy, vol. 2018, 12 pages, 2018.
View at: Publisher Site | Google Scholar
T. Rojviroon, O. Rojviroon, and S. Sirivithayapakorn, “Photocatalytic decolourisation of dyes using TiO2thin film photocatalysts,” Surface Engineering, vol. 32, no. 8, pp. 562–569, 2016.
View at: Publisher Site | Google Scholar
M. Long, J. Wang, H. Zhuang, Y. Zhang, H. Wu, and J. Zhang, “Performance and mechanism of standard nano-TiO₂ (P-25) in photocatalytic disinfection of foodborne microorganisms – Salmonella typhimurium and Listeria monocytogenes,” Food Control, vol. 39, pp. 68–74, 2014.
View at: Publisher Site | Google Scholar
J. Yuan, E. Wang, Y. Chen, W. Yang, J. Yao, and Y. Cao, “Doping mode, band structure and photocatalytic mechanism of B–N-codoped TiO₂,” Applied Surface Science, vol. 257, no. 16, pp. 7335–7342, 2011.
View at: Publisher Site | Google Scholar
K. Nakata and A. Fujishima, “TiO₂ photocatalysis: design and applications,” Journal of Photochemistry and Photobiology C: Photochemistry Reviews, vol. 13, no. 3, pp. 169–189, 2012.
View at: Publisher Site | Google Scholar
F. Zhang, R. Jin, J. Chen et al., “High photocatalytic activity and selectivity for nitrogen in nitrate reduction on _Ag/TiO catalyst with fine silver clusters,” Journal of Catalysis, vol. 232, no. 2, pp. 424–431, 2005.
View at: Publisher Site | Google Scholar
H. O. N. Tugaoen, S. Garcia-Segura, K. Hristovski, and P. Westerhoff, “Challenges in photocatalytic reduction of nitrate as a water treatment technology,” Science of The Total Environment, vol. 599-600, pp. 1524–1551, 2017.
View at: Publisher Site | Google Scholar
EPA, Final aquatic life ambient water quality criteria for ammonia-freshwater, 2013, https://www.federalregister.gov/documents/2013/08/22/2013-20307/final-aquatic-life-ambient-water-quality-criteria-for-ammonia-freshwater-2013.
L. Li, Z. Xu, F. Liu et al., “Photocatalytic nitrate reduction over Pt–Cu/TiO₂ catalysts with benzene as hole scavenger,” Journal of Photochemistry and Photobiology A: Chemistry, vol. 212, no. 2-3, pp. 113–121, 2010.
View at: Publisher Site | Google Scholar
J. Sá, C. A. Agüera, S. Gross, and J. A. Anderson, “Photocatalytic nitrate reduction over metal modified TiO₂,” Applied Catalysis B: Environmental, vol. 85, no. 3-4, pp. 192–200, 2009.
View at: Publisher Site | Google Scholar
T. Yang, K. Doudrick, and P. Westerhoff, “Photocatalytic reduction of nitrate using titanium dioxide for regeneration of ion exchange brine,” Water Research, vol. 47, no. 3, pp. 1299–1307, 2013.
View at: Publisher Site | Google Scholar
K. Kobwittaya and S. Sirivithayapakorn, “Photocatalytic reduction of nitrate over TiO₂ and Ag-modified TiO₂,” Journal of Saudi Chemical Society, vol. 18, no. 4, pp. 291–298, 2014.
View at: Publisher Site | Google Scholar
J. M. A. Freire, M. A. F. Matos, D. S. Abreu et al., “Nitrate photocatalytic reduction on TiO₂: metal loaded, synthesis and anions effect,,” Journal of Environmental Chemical Engineering, vol. 8, no. 4, article 103844, 2020.
View at: Publisher Site | Google Scholar
S. Cao, R. Du, Y. Peng, B. Li, and S. Wang, “Novel two stage partial denitrification (PD)-Anammox process for tertiary nitrogen removal from low carbon/nitrogen (C/N) municipal sewage,” Chemical Engineering Journal, vol. 362, pp. 107–115, 2019.
View at: Publisher Site | Google Scholar
L. M. Santos, W. A. Machado, M. D. França et al., “Structural characterization of Ag-doped TiO₂ with enhanced photocatalytic activity,” RSC Advances, vol. 5, no. 125, pp. 103752–103759, 2015.
View at: Publisher Site | Google Scholar
S. Krejčíková, L. Matějová, K. Kočí et al., “Preparation and characterization of Ag-doped crystalline titania for photocatalysis applications,” Applied Catalysis B: Environmental, vol. 111-112, pp. 119–125, 2012.
View at: Publisher Site | Google Scholar
K. Gupta, R. P. Singh, A. Pandey, and A. Pandey, “Photocatalytic antibacterial performance of TiO₂ and Ag-doped TiO₂ against S. aureus. P. aeruginosa and E. coli,” Beilstein Journal of Nanotechnology, vol. 4, pp. 345–351, 2013.
View at: Publisher Site | Google Scholar
N. Krasae and K. Wantala, “Enhanced nitrogen selectivity for nitrate reduction on Cu–nZVI by TiO₂ photocatalysts under UV irradiation,” Applied Surface Science, vol. 380, pp. 309–317, 2016.
View at: Publisher Site | Google Scholar
M. Ahamed, M. A. M. Khan, M. J. Akhtar, H. A. Alhadlaq, and A. Alshamsan, “Ag-doping regulates the cytotoxicity of TiO₂ nanoparticles via oxidative stress in human cancer cells,” Scientific Reports, vol. 7, no. 1, p. 17662, 2017.
View at: Publisher Site | Google Scholar
Y. Luo, S. Yu, B. Li et al., “Synthesis of (Ag,F)-modified anatase TiO2nanosheets and their enhanced photocatalytic activity,” New Journal of Chemistry, vol. 40, no. 3, pp. 2135–2144, 2016.
View at: Publisher Site | Google Scholar
R. Saravanan, D. Manoj, J. Qin et al., “Mechanothermal synthesis of Ag/TiO₂ for photocatalytic methyl orange degradation and hydrogen production,” Process Safety and Environmental Protection, vol. 120, pp. 339–347, 2018.
View at: Publisher Site | Google Scholar
N. T. Minh and B.-K. Lee, “Feasibility of silver doped TiO₂/glass fiber photocatalyst under visible irradiation as an indoor air germicide,” International Journal of Environmental Research and Public Health, vol. 11, pp. 3271–3288, 2014.
View at: Google Scholar
L. Lu, G. Wang, Z. Xiong et al., “Enhanced photocatalytic activity under visible light by the synergistic effects of plasmonics and Ti³⁺-doping at the Ag/TiO2- heterojunction,” Ceramics International, vol. 46, no. 8, pp. 10667–10677, 2020.
View at: Publisher Site | Google Scholar
A. Herissan, J. Meichtry, H. Remita, C. Colbeau-Justin, and M. Litter, “Reduction of nitrate by heterogeneous photocatalysis over pure andradiolytically modified TiO₂ samples in the presence of formic acid,” Catalysis Today, vol. 281, 2016.
View at: Google Scholar
L. Elsellami, F. Dappozze, A. Houas, and C. Guillard, “Effect of Ag⁺ reduction on the photocatalytic activity of Ag-doped TiO₂,” Superlattices and Microstructures, vol. 109, pp. 511–518, 2017.
View at: Publisher Site | Google Scholar
X. F. Lei, X. X. Xue, and H. Yang, “Preparation and characterization of Ag-doped TiO₂ nanomaterials and their photocatalytic reduction of Cr(VI) under visible light,” Applied Surface Science, vol. 321, pp. 396–403, 2014.
View at: Publisher Site | Google Scholar
D. Zhang, B. Wang, X. Gong, Z. Yang, and Y. Liu, “Selective reduction of nitrate to nitrogen gas by novel Cu₂O-Cu₀@Fe₀ composite combined with HCOOH under UV radiation,” Chemical Engineering Journal, vol. 359, pp. 1195–1204, 2019.
View at: Publisher Site | Google Scholar
W. Gao, R. Jin, J. Chen et al., “Titania-supported bimetallic catalysts for photocatalytic reduction of nitrate,” Catalysis Today, vol. 90, no. 3-4, pp. 331–336, 2004.
View at: Publisher Site | Google Scholar
F. Zhang, Y. Pi, J. Cui, Y. Yang, X. Zhang, and N. Guan, “Unexpected selective photocatalytic reduction of nitrite to nitrogen on silver-doped titanium dioxide,” The Journal of Physical Chemistry C, vol. 111, no. 9, pp. 3756–3761, 2007.
View at: Publisher Site | Google Scholar
S. Parastar, S. Nasseri, S. H. Borji et al., “Application of Ag-doped TiO2nanoparticle prepared by photodeposition method for nitrate photocatalytic removal from aqueous solutions,” Desalination and Water Treatment, vol. 51, no. 37-39, pp. 7137–7144, 2013.
View at: Publisher Site | Google Scholar
J. Huang, L. Ding, Y. Xi et al., “Efficient silver modification of TiO₂ nanotubes with enhanced photocatalytic activity,” Solid State Sciences, vol. 80, pp. 116–122, 2018.
View at: Publisher Site | Google Scholar
R. Qian, H. Zong, J. Schneider et al., “Charge carrier trapping, recombination and transfer during TiO₂ photocatalysis: an overview,” Catalysis Today, vol. 335, 2018.
View at: Google Scholar
S. Buda, S. Shafie, S. A. Rashid, H. Jaafar, and N. F. M. Sharif, “Enhanced visible light absorption and reduced charge recombination in AgNP plasmonic photoelectrochemical cell,” Results in Physics, vol. 7, pp. 2311–2316, 2017.
View at: Publisher Site | Google Scholar
B. Xin, L. Jing, Z. Ren, B. Wang, and H. Fu, “Effects of simultaneously doped and deposited Ag on the photocatalytic activity and surface states of TiO₂,” The Journal of Physical Chemistry B, vol. 109, no. 7, pp. 2805–2809, 2005.
View at: Publisher Site | Google Scholar
G. Tokazhanov, E. Ramazanova, S. Hamid, S. Bae, and W. Lee, “Advances in the catalytic reduction of nitrate by metallic catalysts for high efficiency and N₂ selectivity: a review,” Chemical Engineering Journal, vol. 384, p. 123252, 2020.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2020 Orawan Rojviroon et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

717

Downloads

703

Citations

International Journal of Photoenergy

New Environmentally Friendly Solar Energy and Hydrogen Storage Materials

Effects of Initial Nitrate Concentrations and Photocatalyst Dosages on Ammonium Ion in Synthetic Wastewater Treated by Photocatalytic Reduction

Abstract

1. Introduction

2. Materials and Methodology

2.1. Ag-TiO2 Photocatalyst Preparation and Characteristics

2.2. Photocatalytic Reduction for Removal

2.3. Selectivity of Photocatalytic Reduction for Removal

3. Results and Discussion

3.1. Ag-TiO2 Nanopowder Photocatalyst Characteristics

3.2. Removal Using Photocatalytic Reduction

4. Conclusion

Data Availability

Conflicts of Interest

Acknowledgments

References

Copyright

2.1. Ag-TiO₂ Photocatalyst Preparation and Characteristics

3.1. Ag-TiO₂ Nanopowder Photocatalyst Characteristics