**Alexsandro Jhones dos Santos 1, Luana Márcia Bezerra Batista 2, Carlos Alberto Martínez-Huitle 1,\*, Ana Paula de Melo Alves 3,\* and Sergi Garcia-Segura 4,\***


Received: 2 December 2019; Accepted: 12 December 2019; Published: 14 December 2019

**Abstract:** Niobium-based metal oxides are emerging semiconductor materials with barely explored properties for photocatalytic wastewater remediation. Brazil possesses the greatest reserves of niobium worldwide, being a natural resource that is barely exploited. Environmental applications of solar active niobium photocatalysts can provide opportunities in the developing areas of Northeast Brazil, which receives over 22 MJ m2 of natural sunlight irradiation annually. The application of photocatalytic treatment could incentivize water reuse practices in small and mid-sized textile businesses in the region. This work reports the facile synthesis of Nb2O5 catalysts and explores their performance for the treatment of colored azo dye effluents. The high photoactivity of this alternative photocatalyst makes it possible to quickly obtain complete decolorization, in less than 40 min of treatment. The optimal operational conditions are defined as 1.0 g L−<sup>1</sup> Nb2O5 loading in slurry, 0.2 M of H2O2, pH 5.0 to treat up to 15 mg L−<sup>1</sup> of methyl orange solution. To evaluate reutilization without photocatalytic activity loss, the Nb2O5 was recovered after the experience and reused, showing the same decolorization rate after several cycles. Therefore, Nb2O5 appears to be a promising photocatalytic material with potential applicability in wastewater treatment due to its innocuous character and high stability.

**Keywords:** advanced oxidation processes; azo dye; sustainable resources; niobium; water reuse; water treatment
