The effect of heating temperature and nitric acid treatments on the performance of Cu- and Zn-based broad spectrum respirator carbons

Impregnated activated carbons (IACs) that are used in broad spectrum gas mask applications have historically contained copper and/or zinc impregnants. The addition of an oxidizing agent, such as nitric acid (HNO3) can be useful in distributing the metallic impregnants uniformly on the activated carbon substrate. In this work, we study IACs prepared from copper nitrate (Cu(NO3)2) and zinc nitrate (Zn(NO3)2) precursors as a function of HNO3 content present in the impregnating solution and as a function of heating temperature. The gas adsorption capacity of the IACs was determined by dynamic flow testing using sulfur dioxide (SO2), ammonia (NH3), hydrogen cyanide (HCN) and cyclohexane (C6H12) challenge gases under dry and humid conditions. The thermal decomposition and distribution of the impregnant on the activated carbon substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis techniques. Relationships between gas adsorption capacity, impregnant distribution and the species of surface impregnants are discussed.

Graphical abstractSEM images of the inner pores of impregnated activated carbon samples prepared using the same precursor. The left and right images were obtained from samples heated at 180 °C and 450 °C respectively.Figure optionsDownload full-size imageDownload high-quality image (52 K)Download as PowerPoint slideHighlights► Nitric acid treatments decreased metal oxide grain size. ► Well dispersed, small grain size impregnants had good gas adsorption capacity. ► Appropriate thermal treatments were key to impregnant phase and performance. ► Zn-based samples with simple chemistry and synthesis were found to perform well.