Niobium pentaoxide (Nb₂O₅) as an efficient photocatalyst for photocatalytic degradation of rhodamine-B

Dyes are widely used in the fabric/textile industry so major sources of environmental pollution are dye wastewater pollutants (Al-Kahtani 2017). Fabric/textile industry wastewater produced intensive organic dyes and the toxicity of these dyes has become a worldwide problem for the aquatic system (Ucker et al. 2021). The greater durability of modern synthetic dyes with their complicated aromatic structure makes biological treatment approaches ineffective (Yang et al. 2012). For the treatment of dye wastewater, currently some other physical and chemical techniques such as coagulation, ultra-filtration, adsorption, and membrane separation are available with limited success (Prado et al. 2008; Zhang et al. 2008; Qamar & Muneer 2009). Rhodamine-B (RB), one of the most important dyes, is used in many industrial processes for dyeing paper and producing a dye laser (Liang & Guo 2010; Topare et al. 2015). It has been experimentally proven that RB is harmful to animals and human beings which causes respiratory tract, irritation of the eyes, and skin. Thus, keeping the harmful effects and hazardous nature of RB, it was measured important to make efficient efforts to degrade RB from an aqueous solution (Akpan & Hameed 2009; Zhou et al. 2011).

The use of advanced oxidation processes (AOPs), in the degradation of the organic pollutants using the photocatalyst, has shown the potential to completely remove the organic and inorganic pollutants apart from the other major technologies available which concentrate the dye on an adsorbent that involves the transfer of the pollutant from a liquid phase to another phase (Kaviyarasu et al. 2013; Fairooz & Ali 2016; Santos et al. 2019). The material's photocatalytic activity and other properties are significantly affected by its crystalline structure (Nunes et al. 2020). In addition, it is common knowledge that the synthesis pathway approach possibly prominent role in determining the structural properties that are ultimately produced (Prado et al. 2021).

The photodegradation of pollutants may benefit from the implementation of an innovative new approach, which makes use of the Nb₂O₅ catalyst. This approach can be applied to a wide variety of semiconductors; in particular, metal oxide semiconductors have high surface areas and unique optical and electrical properties that make them ideal for use in photocatalytic applications. Thermodynamically stable and highly corrosion-resistant, niobium pentoxide (Nb₂O₅) has the potential to be used as a catalytic oxidation catalyst for organic molecules in aqueous conditions (Hashemzadeh et al. 2013; Osman et al. 2021). Nb₂O₅ has strong corrosion resistance and low toxicity, which has piqued the interest of the research community. This compound has a wide range of uses, including catalysis, solar cells, gas sensors, and electrochromic, to name a few. It has also been the subject of some recent studies (Brites et al. 2011; Carvalho et al. 2020). Dehydration, hydration, etherification, hydrolysis, condensation, alkylation, dehydrogenation, and oxidation are only a few of the many processes for which Nb₂O₅ is utilized as a catalyst (Topare et al. 2013; Jesus et al. 2021).

Visible-light irradiation photocatalyst development and comparison of photocatalytic activity of various photocatalysts for dye degradation have been the subject of substantial research in recent years (Moreira & Borges 2018). One of the prospective photocatalysts, Nb₂O₅, which has a band gap energy of 3.4 eV and is comparable to that of TiO₂, demonstrates strong photocatalytic activity in the process of dye photodegradation (Reeta et al. 2018). This makes it one of the most promising photocatalysts. The use of Nb₂O₅ for the photodegradation of pollutants, on the other hand, is not widely investigated in the published research (Paris et al. 2020; Troncoso & Tonetto 2021). In the present study, Nb₂O₅ was used as a photocatalyst and the photocatalytic activity of this material on RB dye was investigated when it was exposed to visible light. To determine the optimal conditions for photocatalytic degradation of RB, the study examined how several parameters, including the starting concentration of RB, the dosage of the catalyst (Nb₂O₅), and the pH of the solution, impacted the process.

RB is widely used in dyeing the fabric used for experimental work. The molecular formula of RB is C₂₈H₃₁ClN₂O₃ and has a molar mass of 479.02. RB dye chemical structure is given in Table 1. The photocatalyst was used as the analytic grade of Nb₂O₅ (99.9%). Various reagent solutions were made up in double-distilled water for the experiments. To control the acidity and alkalinity of the solutions, 0.1 N HCl/0.1 N NaOH was utilized.

Table 1

RB chemical structure

Name of dye .	Chemical structure .
Rhodamine-B (RB)

Name of dye .	Chemical structure .
Rhodamine-B (RB)

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The experiments were carried out by employing Nb₂O₅ as a photocatalyst onto RB when exposed to visible light. The degradation efficiency was evaluated by the influence of process parameters including catalyst (Nb₂O₅) dosage (0.25, 0.5, 0.75, 1.0, and 1.25 g/l), initial RB concentration (10, 20, 30, and 40 mg/l), and the solution pH (3, 5, 7, 9, and 11) were studied.

In the degradation of RB, the Nb₂O₅ was used as a catalyst. The degradation of RB is facilitated in the presence of a catalyst as experimental results confirmed. With an increase in catalyst dose up to an optimum loading, the initial rate of degradation of RB increased. Further, it showed no effect on the degradation of RB, as a result of an increase in the catalyst dose. As the rate of degradation of RB decreased, the initial RB concentration increased. It also shows that the maximum degradation of RB was observed at optimal conditions, i.e. RB initial concentration is 10 mg/l, catalyst (Nb₂O₅) dosage is 1 mg/l, and the pH is 11.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

This research work was funded by Institutional Fund Projects under grant no. (IFPIP:1296-961-1443). The authors gratefully acknowledge the technical and financial support provided by the Ministry of Education and King Abdulaziz University, DSR, Jeddah, Saudi Arabia.