Flash Joule Heating Equipment: Zinc oxide:copper oxide composites for photocatalysis obtained by rapid Joule heating

Background

These nanostructures have a wide range of applications. In this work, we will focus on photocatalytic activity. Nowadays, catalytic processes are probably one of the hottest topics as they are involved in serious environmental issues such as the production of hydrogen through water splitting and the elimination of pollutants from water. Photocatalytic technology plays a central role in water treatment processes as the problem of water pollution by effluents is increasing due to the continuous expansion of the textile, leather, paper and ink industries.

The main point of this paper

Importance of transition metal oxides (TMOs):

Wide range of applications, versatility and physical properties (e.g., conductivity, magnetism, luminescence).

Understanding of key factors such as carrier concentration, recombination rate, mobility and defect structure is critical for applications.

Nanostructure research:

Nanowires and nanostructures have been studied for their properties and applications that differ from those of bulk materials.

The increased surface-to-volume ratio makes them more effective in areas such as gas sensing or photocatalysis.

Material selection criteria:

Stability, low toxicity, non-criticality, low price and versatility are key.

Fabrication of hybrid or composite structures:

This is an active area of research, especially in photocatalysis or sensing applications.

Nanostructure growth methods:

Conventional methods such as CVD and VLS are time consuming and costly.

Resistance heating is a fast and cost-effective alternative method to grow nanostructures by utilizing the Joule energy loss generated by passing an electric current through a metal wire.

The method forms a core/shell structure by oxidizing the wire. The oxidation process is fast, which reduces processing time and cost while yielding high-density nanostructures.

Zinc oxide and copper oxide semiconductor oxide nanostructures based on resistive heating and electrochemical etching: a study of photocatalytic efficiency enhancement

Semiconductor oxides for photocatalytic processes:

Different series of semiconductor oxides are ideal materials for photocatalytic processes.

Challenges in photocatalytic efficiency:

Improving the efficiency of photocatalytic process under sunlight irradiation is a challenge.

Research:

Growth and characterization of semiconductor oxide nanostructures and composites based on ZnO and CuO families are presented.

Growth method:

The corresponding oxides were generated by resistive heating of Zn and Cu wires.

Combined with electrochemical corrosion of Zn.

Material Characterization:

Characterization of the materials using scanning electron microscopy and optical spectroscopy techniques.

Advantages of the research methodology:

Improved degradation efficiency.

Cheap, easy and fast growth method.

These features help to extend the photocatalytic process beyond the laboratory.

Summarize

All sample series obtained by the Joule heating method grew a homogeneous layer of metal oxides within a very short processing time (about tens of seconds). The efficiency of this method is unquestionable compared to other more expensive and time-consuming methods. For our chosen photocatalytic application, another advantage of this growth method over methods such as using suspended nanoparticles is the ease of recycling. The treated liquid does not need to go through any subsequent process to collect the catalyst, as the catalyst filaments are easily recycled. This allows the photocatalyst to be characterized after treatment.

After finding the optimal growth conditions, the ZnO/CuO composite samples exhibited properties that are interesting for photocatalysis. The configurations that gave the best results were the Zn-Cu braided wires, due to their remarkable and homogeneous nanostructured coating and the slight mixed doping at the interface between the oxide layers. Photocatalytic tests using Rhodamine B as a simulated pollutant showed that these samples produced significant degradation under both UV and visible light irradiation. Light exposure to the zinc-copper braid, together with the formation of oxides on its surface by Joule heating, promoted the enhancement of the electrochemical corrosion that produced the zinc oxide nanorods, which contributed to the overall photocatalytic process.