# Copper Phthalocyanine Chemiresistors as Industrial NO2 Alarms

## TL;DR

A new copper-based sensor detects dangerous NO2 leaks in industrial settings, but is not suitable for environmental monitoring.

## Contribution

A novel chemiresistor using copper(II)phthalocyanine (CuPc) is developed for industrial NO2 leak detection with strong response above 87 ppb.

## Key findings

- The sensor shows a strong response to NO2 above ~87 ppb, with resistance dropping by a factor of 870 at 1 ppm.
- The sensor is not suitable for environmental monitoring due to weak responses at low pollution levels.
- The strong NO2 response is attributed to CuPc doping and differences in film morphology.

## Abstract

We present a chemiresistor sensor for NO2 leaks. The sensor uses the organometallic semiconductor copper(II)phthalocyanine (CuPc), and is more easily manufactured and characterised than previously described organic transistor gas sensors. Resistance R is high but within the range of modern voltage buffers. The chemiresistor weakly responds to several gases, with either a small increase (NH3 and H2S) or decrease (SO2) in R. However, the response is low at environmental pollution levels. The response to NO2 also is near-zero for permitted long-term exposure. Our sensor is, therefore, not suited for environmental monitoring, but acceptable environmental pollutant levels do not interfere with the sensor. Above a threshold of ~87 ppb, the response to NO2 becomes very strong. This response is presumably due to the doping of CuPc by the strongly oxidising NO2, and is far stronger than for previously reported CuPc chemiresistors. We relate this to differences in the film morphology. Under 1 ppm NO2, R drops by a factor of 870 vs. non-polluted air. An amount of 1 ppm NO2 is far above the ‘background’ environmental pollution, thereby avoiding false alarms, but far below immediately life-threatening levels, thus giving time to evacuate. Our sensor is destined for leak detection in the nitrogen fertiliser industry, where NO2 is an important intermediate.