Caroline Hroncich

Finding more effective methods for classifying recycling is key for environmental protection. This ensures that all recyclable waste like plastic and glass, are properly disposed.

Researchers from Hefei University of Technology in China are searching for more effective methods of analyzing recyclable waste. The team 

using laser-induced breakdown spectroscopy (LIBS) as a tool for categorizing recyclable materials.

LIBS is an atomic emission spectroscopy technology that detects the elemental composition of the sample based on emission spectra, the researchers wrote in the study. Unlike many spectroscopic techniques, LIBS technology is not impacted by the environment or lighting, or other factors such as the sample’s shape or color.

 spoke with Lei Yang, an author of the study and a professor at Hefei University of Technology, about how LIBS technology could improve the classification of recyclable items.

Why is classifying waste a growing challenge for environmental protection?

The growth of the population and the improved living standards have led to a sharp increase in both the categories and quantities of waste. Excess waste will cause serious environmental pollution and loss of resources if it is not properly managed and disposed of. In fact, many so-called wastes also have a significant value if recycled. By using waste classification management, we can maximize the utilization of waste resources, reduce the amount of waste disposal, and improve the quality of the general living environment. Waste classification is an urgent issue that needs to be addressed for environmental protection.

A diagram of the LIBS experiment system. Courtesy of Lei Yang. 

Why is laser induced breakdown spectroscopy a good technique for identifying and classifying recyclables?

LIBS is a technology for identifying the elemental composition of the sample. The purpose of identifying and classifying waste is to reduce environmental pollution, and more importantly, to reuse recyclable waste resources. Resource reuse is generally classified based on the composition of waste. Therefore, identifying and classifying methods based on composition analysis will yield high accuracy in waste sorting. Compared to other methods, LIBS technology is not affected by the ambient environment and light, sample shape, and color, and without preprocessing of the sample, which can provide automatic real-time detection, high-precision identification, and classification for recyclable waste.

What other methods are typically used to analyze waste and why is LIBS better?

The methods based on the differences in physical properties of waste—such as electrostatic separation and eddy current separation-—image-based waste classification method, and artificial classification method, are used to analyze waste. Their classification results are inaccurate due to the influence of background, light, geometry, color of waste, and other factors. Infrared spectroscopy, hyperspectral imaging, and fluorescence spectroscopy are also used to analyze waste, but these techniques need to have clean and prepared waste samples in advance and therefore cannot realize automated real-time detection. Compared to these methods, LIBS is not affected by the ambient environment and waste samples and provides fast and accurate analysis, which gives it an advantage in waste classification over other analytical techniques.

A breakdown of how the research team classifies recyclable waste. Courtesy of Lei Yang. 

What challenges did you face during this research?

In our work, it is a challenge to use only a LIBS system without adding other auxiliary instruments to collect spectra of plastics, glass, and other wastes. However, surprisingly, for most of the waste samples, a simple LIBS system can collect sufficient useful spectral information for sample identification and classification.

We are continuing our research in this area. Firstly, we will increase the category and quantity of test waste. Secondly, the waste subclassification will be mainly researched to meet the needs of refined classification for waste recycling and processing factories. Furthermore, we hope to deepen the understanding of transparent glass detection with LIBS.

This interview has been lightly edited for length and clarity.

Articles

Lei Yang, a professor at Hefei University of Technology, outlines how her team is using laser induced breakdown spectroscopy (LIBS) to analyze recycling. 

Seeking More Effective Methods for Recyclable Waste Classification

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 

a group of researchers from the Institute of Atomic and Molecular Physics in China studied excited state intramolecular proton transfer (ESIPT) for the design of hydrophobic florescent probes (1).

ESIPT is a process where a molecule, when excited by light energy, undergoes a proton transfer within itself. In its ground state, the molecule has a stable proton position (donor site). When excited, the proton moves to another location within the molecule (acceptor site), leading to dual emission with different wavelengths upon return to the ground state. ESIPT has broad applications in chemistry and biology, and it is used for designing novel fluorescence-based probes.

Florescent probes are widely used in life sciences research due to their large Stokes shift, along with their high analytical sensitivity and selectivity, the researchers wrote. In this study, the scientists examined 3-hydroxy-2-(6-Methoxynaphthalen-2-yl)-4H-chromen-4-one (MNC) in water and 1,4-dioxane.

The scientists dissolved the MNC in water and 1,4 dioxane before examining the properties of the mixture in a PerkinElmer Lambda 950 and RF5301 fluorescence spectrophotometer.

The scientists found that in an excited S1 state, there is a strengthening of hydrogen bonds, indicating a trend towards excited proton transfer. Raman spectra and potential energy surface data confirm that MNC undergoes a process known as ESIPT in both solutions, with some modifications in the water solution.

The fluorescence quenching observed is not due to the closure of the ESIPT channel but rather the stacking of π-π bonds.

“The results demonstrate that MNC can undergo ESIPT process in water. The proton transfer mechanism of MNC in water is modified,” the researchers wrote. “Moreover, the fluorescence extinction of MNC in water is associated with molecular stacking in the aggregated state. It facilitates that the design of innovative hydrophobic fluorescent probes and organic fluorescent molecules.”

Wan, Y.; Li, Q.; Zhu, L.; Wan, Y.; Yan, L.; Guo, M.; Yin, H.; Shi, Y. Reconsideration of the ESIPT OFF Mechanism for Fluorescent Probe MNC in Aqueous Solution. 

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Researchers from the Institute of Atomic and Molecular Physics in China looked at MNC dissolved in water and 1,4-dioxane.  

Excited State Intramolecular Proton Transfer of MNC for Florescent Probes

The classification of recyclable waste is a challenge for environmental protection. Properly classifying refuse means that it is less likely to be contaminated by other waste during the recycling process and can effectively be reused.

A group of researchers at Hefei University of Technology in China, are using laser-induced breakdown spectroscopy (LIBS) technology for the classification and identification of recyclable waste (1). The scientists outlined their findings in the journal 

LIBS is an atomic emission spectroscopy technology that detects the elemental composition of the sample based on emission spectra, the researchers wrote in the study. Unlike many spectroscopic techniques, LIBS technology is not impacted by the environment or lighting, or other factors such as the sample’s shape or color. LIBS is already used to classify iron ore, coal, plastic, ceramics, and more, the authors wrote, which makes it ideal for classifying waste. More traditional methods of waste classification include gravity separation, magnetic separation, and electrostatic separation. These methods are often only able to detect a few categories of waste.

“We have used LIBS technology for the first time to identify and classify recyclable waste,” said Lei Yang, a study author and professor at Hefei University, in a 

. “This method has accurate, reliable, fast detection results, and can achieve automatic detection.”

The researchers analyzed the spectra of 80 recyclable waste samples and using LIBS classified each sample into paper, plastic, metal, glass, textile, and wood. From there, the team further classified each sample into a more specific sub-category. 

The team also used machine learning (ML) including linear discriminant analysis (LDA) and random forest (RF) to further classify the waste. ML involves the use of algorithms to learn from data to classify samples without being explicitly programmed to do so. LDA is a supervised classification method that aims to find the linear combination of features that best separates different classes by maximizing the ratio of between-class variation to within-class variation. RF is an ensemble learning method that constructs multiple decision trees during training and combines their outputs to improve classification accuracy, while combining the individual predictions from multiple classifier models to arrive at a final classification decision.

While LIBS proved to be a promising technology for categorizing waste, there’s still more work to be done. In the future, they plan on increasing the number of waste samples and incorporating new types of waste such as kitchen waste, they wrote in a press release.

“What surprised us the most was that by using LIBS technology for classification and recognition without any preprocessing of the waste object, the results are satisfactory,” Yang said.

1. Yang, L.; Xiang, Y.; Li, Y.; Bao, W.; Ji, F.; Dong, J.; Chen, J.; Xu, M.; Lu, R. Identification and Classification of Recyclable Waste Using Laser-Induced Breakdown Spectroscopy Technology. 

A group of scientists in China are using LIBS technology to help accurately classify recyclable waste. 

Laser Induced Breakdown Spectroscopy to Classify Recycling

Spectroscopic techniques are helping scientists better analyze ancient manuscripts made from papyrus.

Derived from the wetland plant that shares its name, this paper-like material was used from 3100 BC until the 11th century AD. While it is most known for its use in ancient Egypt, papyrus was also widely used throughout southern Italy, the Mediterranean, and the Roman empire.

Arzak Mohamed, a PhD student and researcher at Macquarie University in Australia, uses analytical methods including X-ray fluorescence (XRF) spectrometry, X-ray diffractometry, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy to analyze ancient papyri and ink.

spoke with Mohamed about her work and how advances in spectroscopy have helped her further the study of ancient texts.

Q: What are some of the key challenges scientists face when analyzing ancient manuscripts?

 Ancient manuscripts could include papyrus sheets, parchment, or paper. I am interested in papyrus sheets, which is the first flexible writing surface invented by ancient Egyptians and was the main writing support for more than 3000 years.

During my work in examination and analysis of archaeological papyrus, I encountered some challenges, like handling fragile papyrus, which need careful treatment during examination and need specific set up of the instruments to avoid any damage can happen during this process. Another challenge could be the limited availability of the analytical instruments. For example, if you need specific instrument, and you cannot find it close your workplace, you need to transfer the samples somewhere else, so museums need to be equipped with non-destructive techniques. There are some limitations that we face with instruments, such as inadequately sized stages especially scanning electron microscopy. Finally, the absence of papyrus standard for calibration for quantification study needs more attention from the analysts.

Arzak Mohamed handling fragile papyrus during her work. To analyze the papyrus, she uses X-ray fluorescence spectroscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Image Credit: Arzak Mohamed.

Q: Talk us through some of the analytical techniques you use to analyze papyrus.

To determine the elemental composition of the inks, pigments, and additives on the surface of the papyrus, I am using X-ray fluorescence spectrometry, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). I am also using X-ray diffractometry to determine the mineralogical composition. In addition, I'm using FTIR to identify the ink's binder and see if any other organic ingredients were employed to prepare the papyrus surface for writing. Raman is also used, particularly when examining black ink, as XRF is unable to characterize carbon, the primary component of lamp black.

I always seek to answer questions such as location of papyrus production, the revealing of fake objects and the dating of unknown samples. I have analyzed papyrus samples from The Egyptian Museum in Cairo, the Egyptian National Library and Archive in Bulaq, and the Macquarie University History Museum and the Chau Chak Wing Museum, both in Australia.

I am also interested in evaluating and testing materials to select the appropriate one for papyrus conservation, so I apply these materials on modern samples and use the analytical methods to assess the effectiveness of these materials on papyrus fibers and their inks.

Q: What recent developments in analytical spectroscopy have helped you improve your work?

 I am happy with the development on the analytical instruments. I think the scientists are doing their best to have portable and non-destructive instrument.

I worked with a Bruker M4 Tornado Micro-XRF spectrometer in quantification of ancient papyrus, as it is a non-destructive technique, and the stage is suitable for big papyrus. In addition to that FT-IR microscopy and portable Raman also facilitate papyrus examination process.

I think the industry section is now aware with the requirements of the archaeological sector, and every day there is a development in the current instruments. I hope these companies can reduce the price of instruments, especially for universities and museums in middle- and low-income countries, to give the researchers in these countries access to updated facilities.

Q: What is the most interesting finding you have come across in your work?

 During analysis of a section of the Book of the Dead from 3rd century BC belonging to the Chau Chak Wing Museum, there was a golden decoration on the papyrus, and I thought it was made from gold, but the analysis revealed there is no gold in the elemental composition of the golden regions, and the main elements is arsenic and sulfur, so the compound is orpiment.

I also analyzed twenty papyri from Macquarie University History Museum, and I have found high concentration of calcium. When we checked the information about these samples, I found that these papyrus fragments were recycled during the Roman Period, and were used in making cartonnage cases, which is a protective casing providing physical and magical protection for mummified bodies. I was able to determine whether the papyri have been extracted from cartonnage by the presence or absence of high concentrations of calcium on papyrus surfaces, and by the presence of the mineral calcite. My publication for this study is under peer review process.

This interview has been edited for length and clarity.

Arzak Mohamed from Macquarie University in Australia broke down how she uses spectroscopy to analyze ancient manuscripts. 

Caroline Hroncich

Articles

Seeking More Effective Methods for Recyclable Waste Classification

Excited State Intramolecular Proton Transfer of MNC for Florescent Probes

Laser Induced Breakdown Spectroscopy to Classify Recycling

Non-Invasive Methods for Studying Papyrus from Ancient Egypt