Photodeposition of Ag nanoparticles on mesoporous LaNaTaO₃ nanocomposites for promotion H₂ evolution

Highlights

• A novel synthesis of mesoporous (0–2 %) Ag /La_0.02Na_0.98TaO₃ was performed via a sol-gel.

• The photocatalytic performance for H₂ evolution was evaluated under UV illumination.

• The XRD and TEM showed Ag NPs (5 nm) photodeposited on the monoclinic structure.

• The obtained H₂ evolution is 3289 μmolg⁻¹ over 1.5 %Ag/La_0.02Na_0.98TaO₃ photocatalyst.

• 1.5 %Ag/La_0.02Na_0.98TaO₃ is greater 40 times than La_0.02Na_0.98TaO₃ photocatalyst.

Abstract

Mesoporous Ag/La_0.02Na_0.98TaO₃ photocatalysts at diverse contents of Ag nanoparticles (NPs) were synthesized through a photoreduction deposition approach. Photocatalytic H₂ evolution from aqueous glycerol solutions as the holes scavenger over mesoporous La_0.02Na_0.98TaO₃ was extremely enhanced by incorporating with Ag NPs as a cocatalyst. The mesoporous La_0.02Na_0.98TaO₃ exhibited low the photocatalytic H₂ evolution ∼ 80 μmolg⁻¹. After incorporation of Ag NPs, the photocatalytic H₂ evolution was increased from 400 to 2966 μmolg^-1 with the increase Ag NPs contents from 0.5 to 1.5 %. The mesoporous 1.5 %Ag/La_0.02Na_0.98TaO₃ photocatalyst exhibits the highest photocatalytic performance, which is greater 40 times than mesoporous pure La_0.02Na_0.98TaO₃ photocatalyst. The improvement of the photocatalytic H₂ evolution was ascribed to the efficient charge carriers transport from the Ag NPs to La_0.02Na_0.98TaO₃, which inhibits the charge carriers recombination through the photocatalytic H₂ evolution. The photoluminescence and photoelectrochemical were used to confirm the enhanced photocatalytic efficiency of Ag/La_0.02Na_0.98TaO₃ photocatalysts.

Introduction

In the past four decades, semiconductor materials as an effective photocatalyst have received substantial attention owing to their extensive potential application in clean energy production such as H₂ evolution and environmental issues such as air purification, water disinfection and purification and detoxification of organic compounds [1]. TiO₂ photocatalyst as a non-toxic, cheap, and efficient for the H₂ evolution and detoxification of water pollutants and air has attracted extremely research interest [[2], [3], [4], [5]]. Unfortunately, limitations such as absorption of UV light only with wide wavelength harvest suppress its considerable potential photocatalysis application [6,7]. Subsequently, scientists have focused their interest to utilize new photocatalyst structures. One of the best structures, tantalates are considered to possess a superior photocatalytic efficiency owing to they exhibit a more negative position conduction bands (Ta 5d orbital) than the conduction bands of titanates (Ti 3d) [8]. A diversity of tantalates, lanthanide tantalates, alkali tantalates and alkaline earth tantalates including La-doped NaTaO₃, closed-shell Ta⁵⁺ ions such as K₃Ta₃Si₂O₁₃, BaTa₂O₆, LnTaO₄ (Ln = Ce, La, Sm, Pr, and Nd), BTa₂O₆ (B = Ba, Sr, and Ca), ATaO₃ (A = Li, Na, and K), SnMn₂O₆ and SnM₂O₇ (M = Ta and Nb), R₃MO₇ (R = La, Ga, Y; M = Nb, Ta), BaTa₄O₁₅, NiOx/In_0.9Ni_0.1TaO₄, Y_1−xTa_xO_1.5+x have been performed [[9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]].

The tantalates structures exhibit rational photocatalytic efficiencies under UV illumination. However, the under visible light illumination, they are still limitations for the demand for a potential application. Precious metal such as Ag and Au possess the surface plasmon resonance (SPR) characteristic, which has developed to be photoinduced upon illumination even at low energy and revealed outstanding photocatalytic efficiency in wide wavelength region [[21], [22], [23], [24]]. As well-known, SPR occurs on the precious metal surface by a combined free electrons oscillation. Subsequently, transient local electromagnetic fields are created by establishing charge carriers rich regions approach the surface. Whenever the noble metals were excited, employing light as an external electromagnetic field, the SP could be photoinduced if their frequencies are corresponding [25]. The synergistic effects of nanocomposite photocatalysts such as Ag-loaded ZnO, Ag-loaded N-TiO₂, Au-loaded TiO₂, Ag-loaded C₃N₄, Ag-loaded AgCl, Ag-loaded TiO₂ and SiO₂, and Au-loaded N-TiO₂, and Au-loaded CdS, Ag/LaTiO₃ and Pt/CaTiO₃ [[26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36]] are playing a substantial role in promoting the photocatalytic efficiency. Loading of Ag NPs on porous nanomaterials is a very effective strategy in designing reactive heterogeneous catalysts because of the good electron-donating ability of Ag NPs and large surface area of the mesoporous support [37,38]. Further, the small spherical Ag NPs with uniform distribution can boost the active site density at the mesoporous support surface, resulting more efficient catalytic activity [37,38].

Basically, the addition of cocatalyst into the photocatalyst exhibits two key factors to enhance the photocatalysis reactions; (i) Fabrication of active sites for reactions either reduction or oxidation and ii) Expedition of photogenerated charge carriers separation. Since both reduction and oxidation reactions take place on the surface of the photocatalyst, the cocatalyst plays an essential role in photocatalysis reaction. However, to the best of our knowledge, mesoporous Ag/La_0.02Na_0.98TaO₃ photocatalysts on the photocatalytic efficiency have not been performed. In this contribution, we focus on the synthesis of mesoporous Ag/La_0.02Na_0.98TaO₃ photocatalysts at diverse Ag NPs contents by a photoreduction deposition approach. The mesoporous 1.5 %Ag/ La_0.02Na_0.98TaO₃ photocatalyst exhibits the highest photocatalytic performance, which is greater 40 times than mesoporous pure La_0.02Na_0.98TaO₃ photocatalyst. The improvement of the photocatalytic H₂ evolution was ascribed to the efficient charge carriers transport from the Ag NPs to mesoporous La_0.02Na_0.98TaO₃, which inhibits the charge carriers recombination through the photocatalytic H₂ evolution. The photoluminescence and photoelectrochemical tools were used to confirm the enhanced photocatalytic efficiency of mesoporous Ag/La_0.02Na_0.98TaO₃ photocatalysts.