Gold nanoparticle fortied bamboo biochar Nanocomposite

Gold nanoparticles due to their specic properties and function have found uses in the eld of engineering to medical sciences. The Gold nanoparticles are always used in conjugation with other chemicals, metals, proteins, and other organic materials. The addition of other conjugates enhances the properties of Gold nanoparticles. As the insertion of metal nanoparticles into an organic matrix effectively increases the specic surface area of such materials, thereby enhancing the desired properties of the material. The term nanocomposite(NCs) is used for material containing an inorganic moiety, with at least one dimension in a nanometre range of 1–100 nm(nanoparticles ) and other materials like metal, ceramics, and polymers. The term “Bionanocomposite" (BNCs)has been assigned to nanocomposites containing a component of biological origin in the mixture. In this work, Bamboo (Bambusa bambos) was used as the organic matrix for the preparation of gold nanoparticle biochar (Au-NPs/BC) nanocomposite. The one-step synthesis approach was used for the treatment of Bamboo with Auric Chloride Salt at room temperature. In addition to the above process, the bamboo was also pyrolyzed at low temperature after treatment, which helped further to reduce the overall cost of the method. This made the method of preparation of the nanocomposite low cost and ecofriendly. Various analytical techniques such as Fourier transform infrared (FT-IR), X ‐ ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X ‐ ray spectroscopy (EDS), and UV–Vis spectroscopy methods were used for the characterization of the synthesized nanocomposite. This nanocomposite was used for the preparation of electrodes and its electrical conductivity was tested. In this method, the nanocomposite was prepared in a good amount via a very simple methodology. The characterization revealed the presence of gold in the nanocomposite, which conrms that this method can be used for the preparation of the (Au-NPs/BC) nanocomposite. low cost of the method. Most notably this method can be used for the synthesis of similar types of BC modied with metal (or metal oxide) nanoparticles and other types of plants. The copper electrode is also prepared in a very simple method and is easy to modify to suite any type of potential sensing application. The potential of these BC materials for energy storage systems, environmental monitoring, catalysis, and biological applications and sensing is signicant. The experiment showed that BC has excellent electrochemical properties, even though reproducibility is currently lacking. Further investigation will be performed to improve the reproducibility of the nanocomposite and nd a suitable application of the modied biochar.


Introduction
Nanocomposites are high-end material, exhibit unusual combinations of properties, and provide new material design opportunities. There is a very high demand for the nanocomposite materials, Because of their attractive potential, there signi cantly improved mechanical and physical properties compared with original grain materials (Camargo et al. 2009;Tasnim et al. 2017). Expected bene ts of nanocomposites include module improvement, exural strength, temperature heat distortion, barrier properties, and other bene ts. Their potential areas of application are very vast from structural, sensing to biomedical application (Jawaid and Swain 2017). Over the last few years, "bionanocomposite" has become a typical term assigned to nanocomposites containing a component of biological origin in mixture with an inorganic moiety, with at least a single dimension in a nanometre range of 1-100 nm (Mousa et al. 2016).
The term "bionanocomposites" was used for the rst time in 2004 also called "nanobiocomposites" (NCs), "green composites," or "biohybrides." (Khan et al. 2017). Bionanocomposites are somewhat similar to nanocomposites, but there are fundamental differences in there preparation methods, properties, functionalities, biodegradability, biocompatibility, and applications (Darder et al. 2007;Shchipunov 2012). These signi cant change in properties is provided by the biological or inorganic components present in the composite (Li et al. 2004). The structure of the nanocomposite typically consists of the matrix material which contains the nanosized reinforcement components in the form of particles, whiskers, bres, nanotubes, etc. New nanocomposites material are being developed based on biochar, Endler, Leonardo W., et al has prepared nickel oxide (BC-NiO) nanocomposite by using Acacia mearnsii plant for the preparation of biochar (Endler et al. 2020). Similar works were done using Cerium Oxide to form nanocomposite using biochar as a base to test for the sonocatalytic performance of the composite (Khataee et al. 2018). The porous structured carbon materials have been used as electrodes due to their properties of high conductivity, large surface area, and the ease of surface modi cations. The unique properties of these carbon materials have generated great interested, but complicated methods of preparation and the high cost have hindered their usability(Chikwendu Okpala). Biochar (BC) is a solid carbonrich residue obtained by thermal decomposition of biomass in a low oxygen environment. The type of biomass used for the preparation of BC signi cantly in uence its composition and thus in uencing its properties (Břendová et al. 2012). The plant's compost of various complex microstructure and networks of highly interconnected channels. These allow e cient distribution of electrolyte in the electrochemical reaction system (Veiga et al. 2017). The other remarkable properties of BC produced by plants is they are nontoxic, heat resistance, and lightweight. Owing to their remarkable properties BC from plants has been utilized to absorb heavy metals, in new battery technologies, and many more. Furthermore, the modi cation done to the BC by the addition of different modi ers like metal and metal oxide nanoparticles can impart new properties to the BC electrode. The combination of Gold nanoparticle (Au-NPs) and biochar (BC) to form nanocomposites improves the e ciency of the electrode (Ferreira et al. 2018). The Gold nanoparticle (Au-NPs) offer unique electrical, optical, mechanical, and magnetic properties different from their bulk form. These properties can be explored in combination with the properties of BC to develop an analytical device to monitor environmental toxicants, catalysis, and many other biological applications. The use of nanoparticles improves the performance of the sensor and their electrochemical activity of the sensors. Here we have developed a simple method for the synthesis of gold nanoparticles biochar nanocomposites. The Bamboo was used to develop the nanocomposite due to its low cost and its ecofriendly properties. The characterization (SEM, XRD, and FTIR) was done to deduce the properties of the Gold nanoparticle, biochar composite (Au-NPs/BC). The prepared copper electrode was modi ed with the (Au-NPs/BC) nanocomposites in a very simple low cost method and can be used for different applications in a very simple method.

Materials
The chemical Used i.e. Auric Chloride were purchased from Himedia chemical reagent Company. All other reagents and chemical compounds were of analytical quality and used without further puri cation. To prepare the electrode 2.0 mm copper wire, copper disk of diameter 8.0 mm, a PVC tube of 10 mm diameter and 50 mm length, the white cement was use as insulator material.G In the experiments, double distilled water was used as a solvent. The Bamboo (Bambusa bambos) was obtained from the botanical garden of Ayurvedic College (Raipur, Chhattisgarh) The specimens were analyzed using Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS) (X-Max) was done to nd the elemental composition. The image was recorded at optimum settings of 20 kV. The powdered sample was used for analysis, which was crushed using a pistil motor. X-ray diffraction patterns (XRD) were obtained on a PANalytical X'pert Pro diffractometer using CuKa as the radiation source. The voltage for the operation was 40 kV, the current was 30mA and the scan rate was 5 min s − 1 . The Bruker instrument was used for Fourier transform infrared ( FT-IR) spectrum analysis. The electrical conductivity was analysized use Digital Multimeter.

Preparation of Gold Nanoparticle bio-char (Au-NPs/BC) nanocomposite
The Bamboo (Bambusa bambos) was obtained from the botanical garden of Ayurvedic College (Raipur, Chhattisgarh). It was used for the production of Bamboo biochar (BC). The synthesis of biochar is schematically presented in Fig. 1. The following steps were followed for the synthesis of (Au-NPs/BC) nanocomposite. The rst step was washing; it was done to remove surface impurities from the stems of Bamboo. In the second step, the bamboo was cut into small pieces of 5 mm length. In the third step, 20 gm of the stem were dipped in aqueous HAuCl4 solution (2.5 mM, 50 mL) for three days, till the stem was completely soaked. For control, instead of the HAuCl4 solution, 1 g of the stems is steeped in distilled water. In the fourth step, the steeped stems were washed and dried, to remove any moisture at 80•C for 24 hours in the oven. In the nal step, the dried stems were subjected to thermal decomposition at 350•C for 2 hours at 2•C/minute in a mu e furnace. Black biochar was obtained at the end of the process, by slow thermal decomposition later it was crushed into ne powder to make the gold Nanoparticle biochar nanocomposite (Au-NPs/BC)(van Zwieten et al. 2010).

Preparation of modi ed electrodes from the nanocomposites
The working electrode was prepared by (Fig. 2.) (A) A 2.0 mm copper (B) copper plate or disk of diameter 8.0 mm (C) PCV casing was added as support, and (D) The insulating and supporting material was added (white cement). At the top 2.0 mm gap was left above the copper disk. The dimensions of the prepared electrode is 10 mm diameter and 50 mm length .The powdered(1 gm) nanocomposite(Au-NPs/BC) and Normal Biochar (Control BC) can be used as a modi er of electrodes in this experiment. The nanocomposite is mixed with Gum Arabic (Conductive and binding polymer) (Bhakat et al. 2018) as a binding agent in the ratio of 3:1. This mixture was lled in the gap in the prepared electrode; the electrode was polished and cleaned before the coating.
Then both the modi ed electrode was dried at 80 o C in an oven. Then this electrode was used for further experiment.

Characterization of Au-NPs/BC nanocomposites
The most appealing aspect of biochar is that it represents a cost-effective, safe, and easy-to-produce process that allows the development of materials with broad applications at a lower cost compared to hydrocarbon or other chemical process materials. While most of the applications are still in their infancy, biochar can already be used with remarkable results in many applications Such applications include soil modi cation, catalysis, water puri cation, and storage of energy and gas. The most recent endeavor for the use of Biochar in developing the Sensors. The biochar derived from plants and plant-based sources are been utilized in many applications. The Pomelo fruit-based sensor is being used to develop high capacity batteries , bamboo (Noman et al. 2014), coffee (Jagdale et al. 2019), sugarcane (Liu et al. 2019), and even rice husk (Ha z et al. 2017)based biochar are used for sensors applications. Biochar has been used as a base material, which can be modi ed with different chemicals and materials Kouchachvili and Entchev 2017;Xiang et al. 2018) (Nanoparticles, Gold, silver). In general, the elemental composition of nanocomposite is affected by the type of plant used for the synthesis and thus effecting its properties (Břendová et al. 2012;Liu et al. 2012). The Change in structure and composition, of biochar, mainly occur during the heat treatment (Veiga et al. 2017). The electrocatalytic properties were analyzed of the Au-NPs/BC-350 nanocomposites prepared from Bamboo (Bambusa bambos) (Crombie et al. 2013). The fresh Bamboo stems were used as the permeation process is employed in the preparation process of the nanocomposite. The low cost and easy availability are some of the reasons to use this plant for the process. The peculation of the HAuCl4 aqueous solution in the precursor is very important to synthesize the nanocomposite. The duct and sieve tubes naturally present in plants stems helps in peculation of the HAuCl4 aqueous solution to the interior of the plants. The impurities and inorganic salts are removed during soaking; this is moreover due to the presence of large amounts of hydrogen ions in the HAuCl4 aqueous solution. The process of thermal decomposition carried on after the above treatment the functional groups such as CO, CO 2 , and H 2 O are removed as volatile elements and thus forming BC (Ahmad et al. 2014;Godlewska et al. 2017). The above process makes the BC more porous and leave the carbon structure (Singh et al. 2017). The decomposition of HAuCl 4 occurs due to heating and this process is further enhanced by the reducing environment formed by the BC. Thus, the nanocomposite of Au-NPs/BC is produced in the process.

(A) SEM and EDS Analysis
As-synthesized BC-350 Its morphology and structure were analyzed using SEM (Fig. 3A). In the SEM images, the sieve tubes and ducts are visible in the biochar. These structure facilities entry of metal salts and chemicals in the biochar. The Au-NPs / BC nanocomposite were powdered and analyzed for the presence of AuNPs in the samples. The Au-NPs / BC-350 SEM images (Fig. 3B) reveal many particles on the BC surface. These ndings suggest the nanoparticles are inserted into the BC by the established method. The SEM image (Fig. 3B) and the EDS (Table 1. (311), standard phase of Au (refer JCPDS le reference no. 04-0784) (Fig. 4). This indicates the biosynthesized gold nanoparticles have high crystallinity. In the XRD patterns of the nanocomposite samples, two large diffraction peaks at 22.3 and 43.4 are due to graphite diffraction pattern (002) and (100) (Singh et al. 2017). Note, the potassium present in bamboo is associated with a self-activation effect which helps to form micro-pores in large amounts (Fahmi et al. 2018). This nding shows that nanocomposites of the Au-NPs / BC are partly graphitized.

(C) FTIR Analysis
Fourier-transform infrared (FTIR) spectroscopy has been used to analyze the effect of thermal decomposition on the surface functional groups of biochar (Fig. 5). Most of the FTIR typically provides features from organic functional groups that are used to examine bio-char organic components. It would be expected the peak at 3420 cm − 1 from organic O-H stretching with the Contribution of any water molecule that may remain in the sample or other hydroxyl group-derived minerals. The band at 2920 cm − 1 is associated with C ≡ C alkyne stretching in hemicellulose. The lignin aromatic group gives rise to asymmetric stretching of C = C at 1576 cm-1 indicating a band of G (Chen et al. 2015). The C-H bending modes decrease at 876 cm − 1 and emit CH4 gas as the temperature rises (Chia et al. 2012). The FTIR analysis con rms all cellulose, hemicellulose, and some lignin content in the bamboo.

Electrochemical behavior of Au-NPs/BC nano-composites
Nanocomposite-modi ed electrodes were built to investigate the electrochemical activity of the modi ed electrode. Both the electrodes the one modi ed with Au-NPs/BC and the control electrode modi ed with BC were tested for comparative resistance using digital multimeter. The Au-NPs/BC electrode showed less resistance compared to BC modi ed electrode. The resistance of both the electrode was less than 5 ohms, which is a mark of a good conductor and thus a good electrode.

Stability and reproducibility of Au-NPs/BC
The study of the stability and reproducibility of the modi ed electrode should be tested for the storage at room temperature. Despite the bene ts of composite nanoparticles-biochar, such as increased biochar production, different surface area, and nanoparticles, the potential risk of metal oxide nanoparticles' environmental and biological toxicity are to be considered (Kahru et al. 2008). Further research should therefore be carried out to improve the stability of the Nano-composites based on the biochar. There are many factors in the production and synthesis processes of biochar-based nanocomposites which can have a signi cant in uence on the properties of the resulting materials. With the production conditions, Biochar properties will change, making the properties of biochar-based nano-composites vary accordingly. the properties and adsorption ability of biochar-based nanocomposites are affected by Biomass type and pyrolysis conditions [27]. The Biochar effects the absorption ability of the sensor, this can be attributed primarily to the different composition and content of biochar lignin, cellulose, hemicellulose, and inorganic salts. Besides the contents, the pyrolysis conditions (thermochemical conversion technology, the temperature of pyrolysis, residue time, etc.) can also have a major in uence on the adsorption performance of biochar based materials [28]. In our assessment, the amount of nanocomposite (Au-NPs/BC) in the electrode is very small (1 gm) there the risk of environmental contamination is very less and the coating is very stable. Table 2 summarizes the biochar modi ed with different materials and their applications in different elds. The modi ed biochar are being used in various electrical and electrochemical applications. The focus of our study is to develop biochar for sensor applications, biochar has been used to develop, Humidity sensor (Ziegler et al. 2017;Jagdale et al. 2019), Pressure sensors, electrochemical sensors (Kalinke et al. 2016;de Oliveira et al. 2017;Liu et al. 2019). The nal approach of this experiment is to utilize the different properties and to develop a sensor from the biochar developed by the above procedure.

Conclusions
In summary, we report a simple, scalable, and cost-e cient method for the preparation of Au-NPs / BC nanocomposites with high surface area, excellent electrical conductivity, and moderately high porosity. This method resulted in a uniform distribution of gold nanoparticles within the BC as shown in SEM and EDS results. The Au-NPs/ BC nanocomposite produced at low (350 o C) temperature and in a mu e furnace. The low temperature and use of simple instruments (instead of Pyrolysis) have contributed to the low cost of the method. Most notably this method can be used for the synthesis of similar types of BC modi ed with metal (or metal oxide) nanoparticles and other types of plants. The copper electrode is also prepared in a very simple method and is easy to modify to suite any type of potential sensing application. The potential of these BC materials for energy storage systems, environmental monitoring, catalysis, and biological applications and sensing is signi cant. The experiment showed that BC has excellent electrochemical properties, even though reproducibility is currently lacking. Further investigation will be performed to improve the reproducibility of the nanocomposite and nd a suitable application of the modi ed biochar.

Declarations
Ethics approval and consent to participate "Not applicable" Consent for publication "Not applicable" Availability of data and material "Not applicable" Figure 1 Steps Involved in Biochar Synthesis The SEM analysis of (a) BC control (b) Au-NPs/BC-350. The presence of Au-NPs is seen in the image (b) Figure 4 XRD analysis of the Biochar sample.

Supplementary Files
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