A Facile Synthetic Method to Obtain Bismuth Oxyiodide Microspheres Highly Functional for the Photocatalytic Processes of Water Depuration

Summary

This article describes a synthetic method to obtain bismuth oxyiodide microspheres, which are highly functional to perform the photocatalytic removal of organic pollutants, such as ciprofloxacin, in water under UV-A/visible light irradiation.

Abstract

Bismuth oxyhalide (BiOI) is a promising material for sunlight-driven-environmental photocatalysis. Given that the physical structure of this kind of materials is highly related to its photocatalytic performance, it is necessary to standardize the synthetic methods in order to obtain the most functional architectures and, thus, the highest photocatalytic efficiency. Here, we report a reliable route to obtain BiOI microspheres via the solvothermal process, using Bi(NO₃)₃ and potassium iodide (KI) as precursors, and ethylene glycol as a template. The synthesis is standardized in a 150 mL autoclave, at 126 °C for 18 h. This results in 2-3 µm-sized mesoporous microspheres, with a relevant specific surface area (61.3 m²/g). Shortening the reaction times in the synthesis results in amorphous structures, while higher temperatures lead to a slight increase in the porosity of the microspheres, with no effect in the photocatalytic performance. The materials are photo-active under UV-A/visible light irradiation for the degradation of the antibiotic ciprofloxacin in water. This method has demonstrated to be effective in interlaboratory tests, obtaining similar BiOI microspheres in Mexican and Chilean research groups.

Introduction

A plethora of semiconductors has been synthesized so far, aiming for photocatalysts with high activity under visible light irradiation, either to degrade organic compounds or to generate renewable energy in the form of hydrogen^1,2. Bismuth oxyhalides BiOX (X = Cl, Br, or I) are candidates for such applications because of their high photocatalytic efficiency under visible light or simulated sunlight irradiation^3,4. The band gap energy (E_g) of bismuth oxyhalides decreases with the increase of the atomic number of the halide; thus, BiOI is the ....

Protocol

NOTE: Please read all the material safety data sheets (MSDS) before using the chemical reagents. Follow all the safety protocols by wearing a lab coat and gloves. Wear UV protection safety glasses during the photocatalysis tests. Be aware that nanomaterials may present important hazardous effects compared to their precursors.

1. Preparation of the BiOI microspheres

1. For Solution 1, dissolve 2.9104 g of bismuth nitrate pentahydrate (Bi(NO₃)₃∙5H₂O) in 60 mL of ethylene glycol in a glass beaker. For Solution 2, dissolve 0.9960 g of KI in 60 mL of ethylene glycol in a....

Results

3D microstructures of BiOI were successfully synthesized by the proposed synthetic method. This was confirmed by the SEM images shown in Figure 1a-c. The microspheres are formed from laminar structures of [Bi₂O₂]²⁺, which are bonded by two iodide atoms¹. The formation of the microspheres depends on the temperature and time of the solvothermal procedure, as these paramet.......

Discussion

We consider the mixture of the precursors as the critical step in the solvothermal synthesis of the BiOI microspheres. A very slow dripping of the KI solution into the Bi(NO₃)₃ solution (at a maximum of 1 mL/min) is crucial to obtain mesoporous microspheres, since it allows the slow formation and self-assembly of the [Bi₂O₂]⁺² slabs, followed by the bonding with the iodide atoms to form the BiOI laminates. The lamellae are the bricks of the microspheres in the solvot.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bismuth(III) nitrate pentahydrate	Sigma Aldrich	383074	ACS reagent, ≥98.0%
Potassium iodide	Sigma Aldrich	746428	ACS reagent, ≥98.0%
Ethylene glycol	Sigma Aldrich	324558	Anhydrous, 99.8%
Ethanol	Meyer	5405	Technical Grade, 96%
Ciprofloxacin	Sigma Aldrich	17850	HPLC, ≥98.0%
Cary 5000 UV-Vis-NIR spectrophotometer	Agilent		Used for the Band gap determination by the Tauc model.
JSM-5600 Scanning Electron Microscope	JOEL		Used for the SEM images.
Autosob-1	Qantachrome Instruments		Used for the determination of surface area and pore diameter.
TOC-L Total Organic Carbon Analyzer	Shimadzu		Used for determination of total organic carbon in water samples.
Bruker AXS D8 Advance - X-ray Diffraction	Bruker		Determination of crystal structure and crystallite size