Influence of the preparation conditions on the morphology and photocatalytic performance Pt-modified hexaniobate composites

Abstract

The preparation of lamellar nanostructures through exfoliation of stacked niobates is an interesting approach to the development of photocatalysts for energy conversion and environmental remediation. These materials exhibit a rich surface chemistry and several nanocomposites can be produced through intercalation or impregnation of suitable precursors. In this work, the influence of the physico-chemical preparation conditions on the photocatalytic activity of Pt-hexaniobate nanocomposites was investigated aiming at the establishment of the main factors that control their photoreactivities. Modification of hexaniobate layers were carried out by adsorption and impregnation methods, using [Pt(NH3)4]Cl2 (Pt1) and H2PtCl6 (Pt2), respectively. The addition of platinum precursors (1% wt.) were performed in the presence of the exfoliating agent tert-butylammonium hydroxide, sNb, or after acidic precipitation followed by resuspension in plain water, eNb. All samples were submitted to photoirradiation to reduce the platinum precursors and the effect of a previous thermal treatment was also evaluated. It was observed that H2 evolution from aqueous methanol solutions is more favored on hexaniobate nanosheets (eNb-Pt1 and eNb-Pt2) instead of scrolled layers (sNb-Pt1 and sNb-Pt2), independent on the platinum precursor. Moreover, residual tert-butylammonium can act as hole scavenger and decrease the degradation rates for methanol oxidation in sNb samples. The curled layers observed for sNb samples seem to favor the photodegradation of cationic species, such as methylene blue. Thermal treatment at 500 °C leads to morphological changes with a decrease of the specific surface area due to restacking of the individual layers along with some curling. As a result, the H2 evolution rates strongly decreases in relation to the non-sintered samples, suggesting that the ‘soft’ photoreduction of platinum precursors is the best method for preparation of these photocatalysts. The correlations between the preparation conditions and the photocatalytic activity for different photoreactions can allow the development of optimized materials for specific applications.

Photoinduced H2 Evolution by Hexaniobate Sheets Grafted with Metal Ions: The Fate of Photogenerated Carriers

“…Bulk K 4 Nb 6 O 17 ·3H 2 O was prepared by the solid reaction method. , Appropriate amounts of Nb 2 O 5 and K 2 CO 3 (molar ratio 2:3) were mixed and heated at 1100 °C for two cycles of 5 h. Partial cation exchange from K + to protons was performed by suspending 3.0 g of the as-synthesized K 4 Nb 6 O 17 ·3H 2 O into 150 mL of 0.2 mol L –1 H 2 SO 4 solution during 3 days . The solid was filtrated, washed with deionized water, and dried at 70 °C.…”

Recent Advances in Niobium-Based Materials for Photocatalytic Solar Fuel Production

“…Layered niobates are composed by a repetition of [NbO 6 ] octahedral units connected through adjacent or opposite sharing edges or corners, resulting in an extended 2D layered arrangement. This configuration is built by the stacking of negative charged layers separated by cations in the interlayer space [11,31]. The first niobate phases were reported in 1955 by Reisman and Frederic [32].…”

“…Recently, our group investigated the influence of the medium, co-catalyst precursor, and heat treatment in the photoactivity of Pt-modified hexaniobate (K 4−x H x Nb 6 O 17 ) for H 2 eVolution [31]. The effect of the Pt(0) precursor and the deposition method (absorption or impregnation) was also investigated.…”

Temperature Dependent Emission Properties of ReI Tricarbonyl Complexes with Dipyrido-Quinoxaline and Phenazine Ligands

“…The simplification follows from previous observation that, at 77 K, (A 298 /A T ) decreases by ca. 16% and (η T /η 298 ) 2 increases by 15% 44,45 and leads to estimated uncertainties of ± 20%.…”