Nanostructure-Directed Chemical Sensing: The IHSAB Principle and the Effect of Nitrogen and Sulfur Functionalization on Metal Oxide Decorated Interface Response

William Laminack,James Gole

doi:10.3390/nano3030469

Abstract

The response matrix, as metal oxide nanostructure decorated n-type semiconductor interfaces are modified in situ through direct amination and through treatment with organic sulfides and thiols, is demonstrated. Nanostructured TiO2, SnOx, NiO and CuxO (x = 1,2), in order of decreasing Lewis acidity, are deposited to a porous silicon interface to direct a dominant electron transduction process for reversible chemical sensing in the absence of significant chemical bond formation. The metal oxide sensing sites can be modified to decrease their Lewis acidity in a process appearing to substitute nitrogen or sulfur, providing a weak interaction to form the oxynitrides and oxysulfides. Treatment with triethylamine and diethyl sulfide decreases the Lewis acidity of the metal oxide sites. Treatment with acidic ethane thiol modifies the sensor response in an opposite sense, suggesting that there are thiol (SH) groups present on the surface that provide a Brønsted acidity to the surface. The in situ modification of the metal oxides deposited to the interface changes the reversible interaction with the analytes, NH3 and NO. The observed change for either the more basic oxynitrides or oxysulfides or the apparent Brønsted acid sites produced from the interaction of the thiols do not represent a simple increase in surface basicity or acidity, but appear to involve a change in molecular electronic structure, which is well explained using the recently developed inverse hard and soft acids and bases (IHSAB) model.

Highlights

There is a substantial need to develop new materials that allow the sensing of chemicals in a broad range of environments
We have recently developed a new concept, inverse hard and soft acids and bases (IHSAB) [1,2,3], that expands on the tenants of the hard and soft acid-base (HSAB) [11] principle and allows the design of novel sensors, as well as catalytic sites
We have found that these metal oxide nanostructures can be readily functionalized, in situ, to create what appear to be metal oxynitride [10,12] and oxysulfide [13] sites

Summary

Introduction

There is a substantial need to develop new materials that allow the sensing of chemicals in a broad range of environments. The ability to manipulate and control charge transport at porous semiconductor micro/nanoporous interfaces, driven by nanostructure-focused Brønsted and Lewis acid-base chemistry, can play a major role in the development of highly responsive, sensitive (ppb), reversible sensors [4,5,6] Within this framework, the creation of novel, highly active, micro-/nano-structured porous extrinsic semiconductor interfaces, their ability to provide readily accessible significant light harvesting surface areas [7] and their ability to be transformed with select nanostructure interactions [1,2,3] provide new avenues for sensing based on energy transfer and transduction [8].

Results and Discussion

Experimental Section

Conclusions