Synthesis of highly fluorescent carbon dots from bread waste and their nanomolar lead ions sensor application

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Abstract

New technology is needed to convert waste material into valuable materials. Keeping this objective in our mind, we have developed a technology for the conversion of bread waste into value nanoparticles. This work describes the synthesis of carbon dots from bread waste and their lead ions sensor application. The synthesized bread waste-derived carbon dots (BCDs) were well characterized by FT-IR, UV–vis, Fluorescence, HR-TEM and Raman spectral techniques. The particle diameter was calculated to be 1.8 ± 0.3 nm by HR-TEM image. The quantum yield of BCDs was calculated to be 22.98 %. Finally, we have applied the BCDs as fluorescence probe for the detection of Pb2+ ions. Interestingly, after the addition of Pb2+ ions into BCDs, the fluorescence was quenched. While adding the Pb2+, the stability of BCDs collapsed due to the binding of Pb2+ with BCDs, which led to aggregate the nanoparticles. Based on the fluorescence quenching, we have quantified the concentration of Pb2+ ions. The good linearity was observed from 4.0 to 56.6 µM, and the detection limit was found to be 8.9 nM (LOD = 3S/m). Further, we have applied this system to river water, tap water and drinking water samples for the detection of Pb2+ ions.

Introduction

In recent days, heavy metal toxicity is received global attention (González-González et al., 2022a, González-González et al., 2022b, González-González et al., 2022c, González-González et al., 2022d). Lead is one of the most abundant and toxic metals (Kim et al., 2012). For example, lead pollution is increasing today because of its wide usage in several sectors including gasoline, paints (González-González et al., 2022a, González-González et al., 2022b, González-González et al., 2022c, González-González et al., 2022d), metallurgies, batteries and pigments (Lin and Qiu, 2011). The continuous use of lead persisting a problem for human beings and also the environment. Nearly, 300 million tonnes of lead mined to date are still circulating in soil and underground water. Lead is a non-biodegradable substance today toxicity to human beings as well as the environment (Andjelkovic et al., 2019). Even low levels of lead can cause a serious threat to the central nervous system in particular infants and also affect their growth and brain development (Goyer, 1993). Lead toxicity can damage many organs including the hematopoietic system, nervous system and kidney (Shukla et al., 2018). The long term exposure of lead contamination in food or water can cause serious health issues including hypertension, diabetes, anemia and reproductive dysfunctions, etc., (Surisetty et al., 2013) Hence, the U.S. Environmental Production Agency has fixed the level of lead in a drinking water is 0.05 mg/L (Kumar and Puri, 2012). Therefore, the sensor of the lead ions is very important to protect the environment and human beings.

The methods correctly applied for the detection of lead including atomic absorption spectroscopy, inductive coupled plasma, mass spectroscopy (Tao et al., 2020), atomic fluorescence spectroscopy and electrochemical method, etc.,(Li et al., 2017) but these methods have some demerits long analysis term, need a trained person to operate, low sensitivity and selectivity and high cost (Wagner et al., 1996) still there is a need to develop a new technology for the detection of lead ions in biological and environmental samples.

The nanotechnology is a leading technology to provide new materials for sensor applications in particularly carbon dots, has received much attention in the field of sensor because of their biocompatibility, easy synthesis (Gokul Eswaran et al., 2021), highly fluorescent, enzyme-mimicking activities (Lopez-Cantu et al., 2022), easy surface functionalization and low photobleaching, etc., (Wang et al., 2021) Recent days, fluorescence nanomaterials are extensively used for sensor applications. Drug the different fluorescent nanomaterials, Carbon dots (C-dots) have emerged and gathered much potential C-dots are a new class of fluorescent nanomaterials, with a diameter, below than 10 nm (González-González et al., 2022a, González-González et al., 2022b, González-González et al., 2022c, González-González et al., 2022d, Xu et al., 2022). It is extensively used in several fields due to their smaller size, unique physical and chemical properties, bio-compatibility, aqueous solubility, etc., (Berenice González-González et al., 2022). These days researched have started to use the waste and biomaterials as starting materials for the synthesis of carbon dots (Wang et al., 2021, Atchudan et al., 2021).

Food waste is a global issue (Obulisamy et al., 2016). European Union people waste almost 90 million tonnes of food every year (Zhu et al., 2013). According to Hindustan Times, around 67 million tonnes of food are wasted in India every year (Ilakovac et al., 2020), which has a value of around 9200 billion Indian rupees and it's enough to feed all of Bihar for a year (Bharucha, 2018). Food wastage cripples a country’s economy to an extent that most of us are unaware. If food is wasted, there is so much waste of water used in agriculture, manpower and electricity lost in food processing industries (Chan et al., 2016) and even contributes to deforestation taking all of into consideration, the actual worth of money per year in India from food wastage is estimated at a whopping Rs. 58,000 crore (Bazilian et al., 2011). Problems associated with such waste includes, severe pollution problems due to high associated chemical and biological oxygen demand (Sarode and Wani, 2017). The bread waste problem is associated with the environmental pollution in the attempt to resolve this problem.

Herein, we are reporting a new protocol for the direct transformation of bread waste into C-dots (BCDs) using the hydrothermal method. The synthesized BCDs were stable for more than seven months. Finally, we have applied the BCDs to the detection of a probe for the Pb2+ ions sensor. Based on the quenching of BCDs fluorescence, we have calculated the concentration of Pb2+ ions. Finally, we applied our BCDs probe for the detection of Pb2+ ions in environmental water samples.

Section snippets

Chemicals required

Monosodium dihydrogen phosphate, di-sodium monohydrogen phosphate, potassium chloride, ferrous chloride, magnesium chloride, sodium chloride, lithium chloride, copper sulphate, nickel sulphate, zinc nitrate, manganese chloride, chromium sulphate and lead nitrate were obtained from Sigma-Aldrich. 0.2 M phosphate buffer solution (pH 3 to pH 12) was prepared by using monosodium dihydrogen phosphate, and the pH was adjusted by using HCl and NaOH. Dialysis tubes with a 29.3 mm diameter with a

Absorbance and fluorescence spectral studies of BCDs

UV–vis spectrum of BCDs exhibits the absorption band at 280 nm (Fig. 1(A) a), revealing that the π-π* electron transition of Cdouble bondC bonds (sp2 domains) (Matsakas et al., 2014). The UV–vis spectrum of only bread extract was obtained at 269 nm (Fig. S1 (a)). Fig. 1A(b) was revealed the fluorescence spectrum of BCDs exhibits the emission maximum at 420 nm with an excitation wavelength of 330 nm. The luminescence property of BCDs is attributed to defect states of the C-dots (surface defect emission)

Conclusion

We have successfully synthesized BCDs from bread waste by hydrothermal method and well characterized by several techniques. The BCDs is stable for seven months. We have utilized BCDs as probe for the detection of Pb2+ ions in different environmental samples. Based on the fluorescence changes of BCDs, We have calculated the detection limit of Pb2+ ions 8.9 nM (LOD = 3S/m). The possible sensing mechanism also was discussed. Interestingly, 100-fold of common interferences did not interfere for the

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

Dr. N. Vasimalai greatly acknowledge to the B.S. Abdur Rahman Crescent Institute of Science and Technology, Chennai 600 048, India for grant of Crescent Seed money (LR.No: CSD/CSM/24/11.03.2021). Mr. S. Gokul Eswaran thanks to B. S. Abdur Rahman Crescent Institute of Science and Technology, Chennai- 600048, India for the award of Junior Research Fellow under the BSA-JRF University fellowship (Lr.No. 411/ Dean(R)/2022/08.04.2022).

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