introductionThere are several ways in which hydrocarbons can enter the soil and contaminate it, such as fuel leakage through storage tanks or transmission lines, rainwater runoff, and car washing places are just two examples. Therefore, testing soil pollution is particularly important in environmental monitoring or land reclamation. Testing total petroleum hydrocarbons (hydrocarbons) through solvent extraction and infrared spectroscopy（TPH）It is a sensitive method, but sample preparation is very complicated. Gas chromatography analysis of extracts can provide higher sensitivity and more detailed component information, but the analysis time is too long. Thermogravimetric analysis and infrared spectroscopy（TG-IR）Combined technology can provide detailed information about the quantity and nature of pollutants without the need for sample preparation. This article will introduce thermogravimetric and infrared spectroscopy（TG-IR）The data and analysis results obtained from the combination of technology.

Experimental Method Take a soil sample with a concentration of approximately10％m/mThe diesel mixture and soil sample are17 milligramPut it inPerkinElmer TGA 4000Thermogravimetric analyzerIn the crucible.TGA 4000passTL8000Transmission lines and10-cmGas pool andPerkinElmer Spectrum™ 100 typeInfrared spectrometer connection. The temperature of the transmission line and gas pool is280℃ to avoid condensation of any heavy organic compounds. The reaction gas for thermogravimetric analysis is nitrogen, with a flow rate of20 mL/minThe flow rate of the balance blowing air is40 mL/min, jointly60 mL/minflow velocityThrough transmission lines and gas pools. with20°C/minofConstant rate from30 °CHeat up tofor800℃. The infrared spectral range is4000-600 cm -1The resolution is8 cm -1, every12 Collect data once per second (sum of each spectrum)4 Secondary interference scanning).Pyris ™ Software is used to control and analyze thermogravimetric data,TimeBase™The software is used to collect and analyze synchronized time-resolved infrared data.

Results and discussion The weight loss curve of the soil sample is shown in the figure1As shown, overall, there were three significant weight loss phenomena: the first one started slightly above room temperature, and the second one began at100Around ℃ and continue until250℃, starting from the third time250Around ℃, until600 Around ℃. In700℃, approximately65%The soil is still in an unburned state, which can be assumed to be mainly composed of inorganic materials.

The average intensity of infrared absorption is determined byGram-SchmidtThermal image, weightlessness curve, and differential curve of weightlessness, as shown in the figure2As shown. The instantaneous absorption concentration of escaping gas detected by infrared is directly proportional to the weight loss rate (among other factors), therefore it can be inferredGram-SchmidtThe thermal image is similar to the differential curve of weightlessness.

image3 Displayed the results of the selected infrared wavenumber region and providedDuring the analysis processRich information. At temperatures slightly above room temperature, an increase in water vapor can be observed, indicating that the soil sample is not dry. The weight loss rate of the first segment on the thermogravimetric curve is approximately5%.Gram-SchmidtThe first peak in the thermal image occurs around230℃ is related to the second weight loss. Inferring from the spectrogram (Figure)4）This is mainly water vapor, fatty hydrocarbons, with a wave number of approximately1745cm-1 A mixture of esters. This indicates that the pollutants may be diesel fuel and a significant portion of biodiesel (fatty acid methyl esters).

image3. Contaminated soil samplesTemperature-basedAbsorption profile diagram. red: Gram-Schmidt tThermal imaging shows overall absorption intensity;dark green: 2933 cm-1 Corresponding nearbyC-Habsorption peak,Corresponding fatty hydrocarbons (diesel and biodiesel);blue: 3015 cm-1Nearby olefinsC-Habsorption peak,Corresponding to unsaturated substances in biodiesel; Black:3800–3700 cm-1;The absorption peak of water between them; Light green:2370 cm-1The absorption peak of carbon dioxide nearby.

The absorption peak of esters overlaps with that of water vapor, but at around3015cm-1placeThere is another selective absorption peak for biodiesel, corresponding to the unsaturated fatty acid chains of olefinsC-HStretching vibration. Plot the relationship between peak intensity and temperature (as shown in the figure)3As shown, the result shows that the peak appeared with a slight backward shift, approximately around240Around ℃. This temperature range includes10%The weight loss is consistent with the known diesel concentration, indicating that this thermogravimetric infrared combined technology can provide a rough test for the quantity and detailed composition information of pollutants.

At higher temperatures, the main gases escaping are carbon dioxide and water, which are generated by the combustion of organic matter in the soil and form the final weight loss component. TimeBasesoftwareAlso draw a superimposed 3D spectrum, as shown in the figure5As shown. A complete dataset showing the evolution of absorption characteristics over time can be clearly seen at a glance

Under the same conditions, throughTG-IRCombined analysis of adding reference to soil samplesdiesel/The mixed sample of biodiesel was used for comparison, and the results are shown in the figure6 And the picture7 As shown. to300Until ℃, the entire sample has evaporated completely, as shown in the figure7 It can be clearly seen that the evaporation of biodiesel lags behind that of fossil diesel. Due to the absence of water in the standard diesel sample, the carbonyl group is subsequently absorbed directly. These data confirm the presence of biodiesel in current soil pollution/Diesel fuel blends provide strong evidence.

ConclusionThermogravimetric analysis provides valuable information for quantitative analysis of samples, but its ability to identify substances is limited. Infrared spectroscopy has the ability to qualitatively analyze escaping gases. This article revealsTG-IRCombined technology can not only determine the amount of diesel present in the soil, but also detect a small portion of biodiesel fuel present. In the field of soil analysis,TG-IRA key advantage of the combination technology is that it does not require sample preparation or solvent extraction, resulting in faster analysis speed and more convenient analysis methods.