Nitrogen-Doped TiO2 Photocatalyst Visible Light Activity

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Solution Overview

Problem

Current TiO2-based photocatalysts are limited by their activity only under UV light due to their large band gap energy, making them ineffective for visible light and sunlight, which are more abundant and renewable sources of radiation, and they often require high-temperature calcination processes that are not suitable for all substrates.

Innovation Solution

A nitrogen-doped TiO2 photocatalyst is developed with a brookite crystalline phase and sufficient nitrogen content to be active under UV, visible light, and sunlight, and can be applied to various substrates, including those not resistant to high temperatures, through a process involving an aqueous suspension of TiO2 nanoparticles, nitrogen doping, calcination, and grinding to create a stable nanometric suspension.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If TiO2-based photocatalysts are used, then high oxidative power and chemical stability are achieved, but they are active only under UV light due to large band gap energy

Engineering Contradiction:

Improvephotocatalytic activity rangeVSAvoidlimitation to UV region

Core Design Contradiction:

Use of energy by moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent applies nitrogen doping to modify the electronic structure of TiO2, changing the band gap energy parameter. The nitrogen atoms substitute oxygen atoms in the TiO2 lattice, creating new energy levels within the band gap that enable visible light absorption. This parameter change transforms the photocatalyst from UV-only activity to visible and UV activity, resolving the contradiction between maintaining high oxidative power and expanding the usable light spectrum.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If high-temperature calcination is performed to obtain nitrogen-doped TiO2, then photocatalytic activity is improved, but substrates not resistant to high temperatures cannot be processed

Engineering Contradiction:

Improvephotocatalytic performanceVSAvoidsubstrate compatibility

Core Design Contradiction:

ProductivityVSAdaptability or versatility

Solution Approach 1:

The patent employs a preliminary doping action during the TiO2 synthesis process itself, rather than requiring subsequent high-temperature calcination. By adding nitrogen sources during hydrothermal or solvothermal synthesis, the nitrogen doping occurs concurrently with crystal formation at lower temperatures. This preliminary action allows the photocatalyst to be prepared with enhanced visible light activity without exposing temperature-sensitive substrates to high-temperature processing.

Inventive Principle:

Principle #10Preliminary action

3Use of energy by moving object

If nitrogen doping is introduced to improve visible light absorption, then photocatalytic activity in visible region increases, but the crystalline structure and stability may be affected

Engineering Contradiction:

Improvevisible light absorptionVSAvoidcrystalline structure stability

Core Design Contradiction:

Use of energy by moving objectVSStability of the object's composition

Solution Approach 1:

The patent applies local quality modification by introducing nitrogen atoms at specific lattice positions (substituting oxygen atoms) rather than uniformly altering the entire crystal structure. The nitrogen doping creates localized electronic states within the band gap while preserving the overall TiO2 crystalline framework. This local quality change enables visible light absorption without compromising the global structural stability of the photocatalyst.

Inventive Principle:

Principle #3Local quality

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 nitrogen-doped TiO2 photocatalyst exhibits enhanced photocatalytic activity in the visible region with a stable brookite phase, maintaining effectiveness over time and allowing application to diverse substrates without requiring high-temperature resistance, thus overcoming the limitations of existing TiO2-based photocatalysts.

Implementation Method 1

the relatively large band gap energy of TiO2 (Eg=3.0-3.2 eV), which absorbs light only with a wavelength smaller than about 387 nm... doping with nitrogen is one of the most effective approaches for improving TiO2 activity in the visible region

Methodology Applied

Scientific EffectBand gap energy modification through doping: Absorption (EM radiation)

Implementation Method 2

The use of light energy in processes of photodecomposition of chemical substances... a fundamental role is played by photocatalysts based on titanium dioxide... suitable for being used as an active photocatalyst not only when subjected to UV light irradiation, but also in the case of irradiation with visible light or sunlight

Methodology Applied

Scientific EffectPhotocatalysis: Photo-oxidation

Data Source

PatentUS11597657B2Nitrogen-doped TiO2 nanoparticles and the use thereof in photocatalysis

Publication Date: 2023.03.07 COLOROBBIA CONSULTING SRL

AI summary

The invention relates to a photocatalyst that is active under irradiation with UV light, visible light and sunlight, comprising a powder or a ready-to-use nanometric suspension of nitrogen-doped TiO2, wherein the brookite crystalline phase is also present and whose doping nitrogen content (% by weight) is sufficient to ensure photocatalytic activity in the visible region. The photocatalyst can be easily applied to substrates of varying nature.