空氣中對人體有害的物質例如: volatile organic compounds (VOCs)、氮氧化物(NOx)、一氧化碳(CO)、粉塵微粒(PM10)…等。由於一氧化碳以及甲醛為最容易於室內接觸到的有毒氣體，所以假若能及時偵測到它們的存在，便可以成功的避免暴露於有毒氣體環境之下，並即時做出相對應的安全措施。
在這篇論文中，使用密度泛函理論(DFT) 模擬不同過渡金屬(鈦，鉻，鎳，鋁) ，取代氧化鋅表面上的鋅金屬。並計算吸附一氧化碳以及甲醛吸附於表面之後的導電度變化以及磁量變化。在一氧化碳偵測方面，我們發現其主要是由配位鍵結 (dative bond) 以及反饋π 鍵 (π-back donation) 與參雜氧化鋅表面作用，作用力的強弱將會影響表面對於一氧化碳感測之性質。我們更進一步發現，參雜金屬的d band center與一氧化碳的前緣分子軌域之能量差距決定上述這兩種作用力的大小與類型。在甲醛偵測方面，我們發現由於配位鍵結以及C-H⋯O氫鍵同時作用於甲醛分子以及參雜氧化鋅表面，進而產生相互協同作用 (cooperative interaction)，另一方面，當反饋π 鍵 (π-back donation) 與C-H⋯O氫鍵同時作用時，則會產生anti-cooperative interaction. 我們的計算結果指出，經由改變能隙 (band gap) 以及磁量變化，參雜鈦以及鋁金屬於氧化鋅表面上分別提高了表面對於一氧化碳以及甲醛的感測靈敏度(sensitivity)，並且可以運用在導電度以及磁量感測器上。

Nowadays controlling indoor air quality is attracting immense research attention since humans are spending more time in the indoor activities. Carbon monoxide (CO) and Formaldehyde (HCHO) is the most common highly toxic gases, which are found in many households and offices. Sensing the toxic gases from atmosphere, which helps us to monitor and obtain more response time to avoid from continuous exposure of CO and HCHO. Therefore in this study, we have performed density functional theory calculations with the generalized gradient approximation for designing the efficient ZnO based sensor. Further, we have considered the different metal atoms such as Cr, Ti, Ni, and Al for doping on the ZnO surface and investigated their electronic and magnetic properties for the detection of CO and HCHO. Our results indicate that the both adsorbents have interacted with surface metal atoms via either dative bond or π-back donation and combination of both. We found that these types of interaction controls their sensing ability. We also analyzed the interaction between adsorbents and the surface metal atoms using density of states (DOS), electron density difference (EDD) contour plots, and change in magnetic moments and compared how the doping of metal atoms affects both electronic and magnetic properties. Our DFT results show that the location of the d band center determines the types of CO interaction for different metal doped ZnO surface and we found that the Ti doped ZnO surface will be the good sensing material for CO compared to others. In the case of HCHO, a cooperative interaction such as C-H⋯O hydrogen bond and dative bond formed between HCHO and different metal doped ZnO surface, except Ti doped surface. Our results proved that the sensing properties of an oxide material can be modified by means of suitable doping. Based on our results we expect that Ti and Al doped ZnO surface will be the suitable material to enhance the sensitivity to detect CO and HCHO at room temperature, respectively.

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