Photodegradation of Organic Pollutants in Seawater and Hydrogen Production via Methanol Photoreforming with Hydrated Niobium Pentoxide Catalysts

Abstract

In this work, the photocatalytic activity of Hydrated Niobium Pentoxide (synthesized by a simple and inexpensive method) was explored in two unknown reactions reported for this catalyst: the photodegradation of phenol in seawater and the photoreforming of methanol. The Hydrated Niobium Pentoxide (Nb1) was synthesized from the reaction of niobium ammoniacal oxalate NH4[NbO(C2O4)2·H2O]•XH2O with a strong base (NaOH). Further treatment of this catalyst with H2O2 led to a light-sensitive Hydrated Niobium Pentoxide (Nb2). The photocatalysts were characterized by XRD, DRS, SEM Microscopy, FTIR-ATR, EDX, and specific surface area (SBET). The characterization results demonstrate that the treatment of Hydrated Niobium Pentoxide sensitized the material, increased the surface area of the material, diminished the average particle size, and modified its surface charge, and formed peroxo groups on the catalytic surface. Although both photocatalysts (Nb1 and Nb2) were active for both proposed reactions, the sensitization of the photocatalyst was beneficial in distinct situations. In the photocatalytic degradation of phenol in seawater, the sensitization of the photocatalyst did not enhance the photocatalytic activity. In both photoreactions studied, the addition of the Pt° promoter readily increased the photocatalytic performance of both photocatalysts; in this case, the sensitized photocatalyst recorded the best results. The presence of OH• radicals was confirmed, and the great contribution of the Pt° promoter was in the increase in OH• radical generation; this increase was more effective in the sensitized photocatalyst. Our work demonstrated a simple and inexpensive way to synthesize niobium photocatalysts that can effectively be used in the photodegradation of phenol in seawater and in the photoreforming of methanol to produce hydrogen.