Preparation of GO-COOH/AuNPs/ZnAPTPP nanocomposites based on the π–π conjugation: Efficient interface for low-potential photoelectrochemical sensing of 4-nitrophenol

Highlights

• Photocurrent of GO-COOH and APTPP or ZnAPTPP by π–π conjugation modified on ITO was better than by amidation reaction.

• GO-COOH/AuNPs/ZnAPTPP nanocomposites were successfully prepared and characterized.

• GO-COOH/AuNPs/ZnAPTPP nanocomposites exhibited the excellent photocurrent response.

• The novel PEC sensor exhibited an excellent photocurrent response to 4-NP.

• The main advantages were simple，high sensitivity, wide concentration range and low detection limit.

Abstract

The GO-COOH/AuNPs/ZnAPTPP nanocomposites were constructed using zinc monoamino porphyrin (ZnAPTPP) through π–π conjugation with carboxylated graphene oxide (GO-COOH) loaded with Au nanoparticles (AuNPs). Prepared materials were characterized by ¹H NMR spectra, UV–vis absorption spectroscopy and electrochemical impedance spectroscopy. ITO electrode surface was modified with the prepared nanocomposites showed a good photocurrent response when the bias potential, −0.1 V was applied. Nanocomposites modified ITO electrode exhibited good photo-response to the 4-nitrophenol (4-NP). ZnAPTPP were excited from HOMO to LUMO under light irradiation, the photoexcited electrons injected into the conduction band of GO-COOH, and then transferred to AuNPs further to the ITO. The presence of GO-COOH and AuNPs improved the separation of photogenerated charges due to their synergetic effect and excellent conductivity. Externally added 4-NP scavenges the photogenerated holes i.e. it acts as a sacrificial electron donor thereby it enhances the photocurrent of the system. Based on this interaction, a novel method for photoelectrochemical detection of 4-NP was developed with a linear range from 0.1 to 15 nmol/L (r = 0.996) and detection limit of 0.04 nmol/L (S/N = 3). Proposed method is simple and sensitive and this was successfully applied for the quantification 4-NP in river water sample matrices.

Introduction

Porphyrins widely exist in the natural world as chlorophyll in plants and hemoglobin in animals and have very good light absorption capacity because of their extended π–π conjugation. Because of their attractive optical properties, ultrafast electron injection ability and high absorption coefficient [1], [2], [3], [4], porphyrins have seen wide spread applications in many areas such as organic synthesis [5], analytical chemistry [6], medicine [7], [8], material science [9], energy sources [10], [11] and photoelectrochemical [12], [13].

Carboxylated graphene oxide (GO-COOH) is a derivative of graphene oxide (GO), which was reportedly prepared based on the nucleophilic substitution reaction between the hydroxyl groups of GO and ClCH₂COOH in NaOH solution [14]. Thus, the –OH and epoxide groups of the GO were converted to –COOH groups, and then obtained COOH [15] functionalized GO. GO-COOH [16] not only shows excellent solubility (as much as 2 mg/mL⁻¹) in water, and the solution has been stable for several months at room temperature, but also has a strong conductivity.

4-nitrophenol (4-NP) is flammable and toxic nitroaromatic compound. The toxic intensity of 4-NP is the highest compared to its homologues (2-NP and 3-NP), which often found in chemical industrial wastewaters as a pollutant [17], [18]. 4-NP is also the hydrolyzate for organophosphorus pesticides [19], which have been widely used for pest control [20]. The health will be damaged by high toxicity of 4-NP when accumulated in the body. Further causes headache, nausea, drowsiness and cyanosis, contact with eyes causes irritation. 4-NP is also existed in others environments [21], [22]. Hence, the detection of 4-NP has received much attention in analytical chemistry and has been widely reported to detect 4-NP with different analytical methods such as: chromatography with spectrophotometry [23], mass spectrometry [24], Fluorescence spectrometry [25] and electrochemical methods [22], [26], [27], [28], [29]. Compared with the traditional methods, a newly developed photoelectrochemical (PEC) [6], [11], [12], [20], [30] detection of biomolecules is the interesting approach in developing analytical method attributed to the efficient charge separation upon photoexcitation and result in highly sensitive photocurrent signal due to the low signal to noise ratio. PEC technique is inherited from the advantages such as remarkable sensitivity, inherent miniaturization, portability and easy integration. The general principal on which the PEC methods developed can be generalized as follows. The semiconductive materials are first irradiated to generate charge carriers. And the added biomolecule [31], [32] as an analyte capture the holes by donating electrons. So that the biomolecules can be oxidized at relatively lower oxidation potential compared to the direct electrochemical oxidation. This technique is highly sensitive to the excitation source and the detection signal due to the low background. A novel PEC biosensor for rapid, sensitive and selective monitoring of 4-NP was developed using functional nanocomposites which consists of ZnAPTPP and GO-COOH with AuNPs through π–π conjugation. Although there are many studies on the electrochemical detection of 4-NP using several modified electrodes, as far as we know, there is no report on the modification of indium tin oxide (ITO) electrode with ZnAPTPP and GO-COOH with AuNPs through π–π conjugation for PEC determination of 4-NP.