Bi(0)-Doped Bismuth Oxyhalide Photocatalysts for Water Purification
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Solution Overview
Problem
Current photocatalysts are ineffective in rapidly decomposing organic contaminants in water under light irradiation, particularly in achieving full oxidation of pollutants like chlorobenzene.
Innovation Solution
A process involving the precipitation of bismuth oxyhalides in an acidic aqueous medium with a reducing agent, such as sodium borohydride, to create Bi(0)-doped bismuth oxyhalides with enhanced photocatalytic activity, which accelerates the oxidation of organic contaminants under UV-Vis and visible light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional photocatalysts like TiO2 are used, then the photocatalytic process is simple and well-established, but the decomposition rate of organic contaminants is slow and full oxidation is not achieved
Solution Approach 1:
The patent uses composite materials by combining bismuth oxyhalide with metallic bismuth particles formed in situ. The Bi(0) dopant creates a dual-phase composite structure (BiOCl/Bi or BiOBr/Bi) that enhances both the decomposition rate and completeness of oxidation. The metallic bismuth particles act as electron sinks, reducing electron-hole recombination and improving photocatalytic efficiency.
Solution Approach 2:
The patent changes the chemical composition parameter by introducing Bi(0) dopant into the bismuth oxyhalide lattice. This doping modifies the electronic structure, extends light absorption to visible range, and creates active sites for complete oxidation. The controlled addition of reducing agent during synthesis precisely controls the Bi(0) content to optimize performance.
2Manufacturing precision
If bismuth oxyhalide is synthesized using hydrothermal method, then crystalline microspheres are formed, but the synthesis process requires high temperature and long time
Solution Approach 1:
The patent performs preliminary action by pre-mixing bismuth salt, halide source, and reducing agent in specific ratios before precipitation. This pre-preparation of reaction components with controlled stoichiometry enables rapid formation of crystalline precipitate with desired structure, eliminating the need for prolonged hydrothermal treatment.
Solution Approach 2:
The patent utilizes phase transition from amorphous precipitate to crystalline structure during the precipitation process itself. By controlling the pH and adding reducing agent during precipitation, the amorphous bismuth oxyhalide transforms in situ to crystalline form with embedded Bi(0) particles, achieving high crystallinity without high-temperature hydrothermal processing.
3Productivity
If reducing agent is added to synthesize Bi(0)-doped bismuth oxyhalide, then photocatalytic activity is enhanced, but the synthesis process becomes more complex
Solution Approach 1:
The patent merges two functions into one step: the reducing agent simultaneously reduces Bi3+ to Bi(0) and serves as a structure-directing agent during precipitation. This combined action simplifies the overall process by eliminating separate reduction and crystallization steps, achieving both Bi(0) doping and crystalline formation in a single precipitation operation.
Solution Approach 2:
The reducing agent performs self-service by automatically regulating the formation of Bi(0) particles during precipitation. The in situ generated Bi(0) particles immediately embed into the forming bismuth oxyhalide crystal lattice, self-organizing the composite structure without requiring additional processing steps or complex equipment.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The Bi(0)-doped bismuth oxyhalides demonstrate high photocatalytic activity, achieving rapid and complete oxidation of organic pollutants, including chlorobenzene, with synergy when combined with hydrogen peroxide, effectively purifying water by mineralizing contaminants.
Implementation Method 1
the addition of a reducing agent to an acidic aqueous reaction mixture comprising bismuth ions and halide salts, especially quaternary ammonium chloride and bromide salts, results in the reduction of some Bi3+ ions to afford Bi(0) doped-bismuth oxyhalide catalysts
Implementation Method 2
Bi(0)-doped bismuth oxyhalides demonstrate high photocatalytic activity, achieving rapid and complete oxidation of organic pollutants, including chlorobenzene, with synergy when combined with hydrogen peroxide, effectively purifying water by mineralizing contaminants
Data Source
AI summary
The invention provides a process for the preparation of bismuth oxyhalide, comprising a precipitation of bismuth oxyhalide in an acidic aqueous medium in the presence of a reducing agent. Also provided are bismuth oxyhalide compounds doped with elemental bismuth Bi(0). The use of Bi(0)doped-bismuth oxyhalide as photocatalysts in water purification is also described.