2D COS Research Articles

The performance and mechanism of HCHO oxidation on Pt/Al2O3 catalysts: The effect of alumina crystalline phase and surface hydroxyls

The performance and mechanism of formaldehyde (HCHO) oxidation on Pt/γ-Al2O3, Pt/θ-Al2O3 and Pt/α-Al2O3 catalysts were investigated, focusing on the impact of OH species, H2O participation and the difference in Pt sites. Characterization revealed that the catalytic performance of Pt/Al2O3 catalysts is predominantly influenced by surface OH rather than other factors. Through CO-TPR and 2D COS analysis, the existence and functions of Pt-OH and Al-OH were distinguished, along with the active and spectator formate species derived therefrom. The introduction of H2O promotes the regeneration of Pt-OH, as well as the migration of intermediate species, which explains the enhancement on catalytic performance under relative humidity. Meanwhile, the proportion of partially oxidized Pt/Pt-terrace/Pt-step would impact the ability of Pt-OH replenishment, further influencing the catalytic activity. These findings highlight the critical role of surface OH species and provide a deeper insight into understanding the OH-effected mechanism in HCHO oxidation.

The role of amino acids in facilitating lead accumulation in microalgae: A quantitative analysis of functional group effects

In aquatic ecosystems, dissolved organic matter (DOM) enhances the adsorption of heavy metals onto microalgae by participating in the formation of algae–heavy metal–DOM ternary complexes, thereby increasing environmental risks. The functional groups in the DOM play a crucial role. However, a quantitative description based on these groups is lacking. This study investigates the effects of amino acids (AAs) with varying functional group ratios on the accumulation of lead (Pb) in Chlorella pyrenoidosa (C. pyrenoidosa) using batch experiments. Isotherm model fitting, and Fourier transform infrared spectroscopy (FTIR) are employed for characterisation. Results indicate that the addition of AAs facilitated Pb enrichment in microalgae. In particular, incorporating lysine (Lys) led to maximum accumulation, reaching 1.45 mmol g−1. The adsorption rate decreased after AA addition, particularly with Lys, dropping form 0.0032 g mg−1 min−1 to 0.0009 g mg−1 min−1. The reaction sequence showed carboxyl groups taking precedence over amino groups. The model developed from the data on Pb adsorption by C. pyrenoidosa following AA addition, demonstrated reliability with an R2 of 0.91 and an F-value of 157.6. Notably this study employed two-dimensional correlation spectroscopy (2D–COS), offering novel insights into the key roles of functional groups and their distinct contributions. These valuable insights contribute to intensive research on the ternary complex of algae − heavy metal − DOM and elucidating their ecological risks.

Single-step propane transformation on vanadium-supported catalyst revealed by operando DRS UV–vis study

The present study investigated the influence of silica support texture on the catalytic performance of VOx/silica catalysts in the selective oxidation of propane. Two- and three-dimensional mesoporous materials, SBA-15 and MCF, were synthesized using hydrothermal methods to create different pore structures. Vanadium (approximately 5 wt%) was incorporated into the silica matrices (MCF, SBA-15) and SiO2 (used as a reference system) through impregnation. The surface composition, valence state, and reducibility of the VOx species accommodated in VOx/silica catalysts were characterized using X-ray diffraction (XRD), diffuse reflectance ultraviolet–visible spectroscopy (UV–vis DRS), temperature-programmed reduction with hydrogen (H2-TPR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) techniques. The catalytic properties of the catalysts were evaluated in the propane selective oxidation conducted at 470 °C, utilizing a mixture of oxidants (N2O and O2). Propane oxidation resulted in propane conversion of 34 %, propene selectivity of 49 %, and propene oxide selectivity of 20 %, corresponding to space–time yield of propene reaching 37 gC3H6 kgcat−1·h−1and propene oxide equal to 20 gPO kgcat−1h−1. The textural properties of the support materials noticeably influenced the stability of the catalysts. The vanadium catalysts supported on three-dimensional mesocellular silica foams (MCF) demonstrated superior activity, achieving turnover frequency (TOF) values of 9.0 × 10−4 s−1 for propene and 6.67 × 10−4 s−1 for propene oxide (PO). The unique three-dimensional ultra-large pores of the MCF material facilitated the generation of significant amounts of propene oxide, along with propene, while minimizing the formation of CO, CO2, and other oxygen-bearing by-products. Operando UV–vis studies supported by two-dimensional correlation analysis (2D COS) were employed to explain the diversity in the catalytic performance of VOx/silica catalysts. It has been found that the oligomeric vanadium species are the active sites in propane oxidative dehydrogenation, whereas the monomeric forms participate in propene oxide formation. Moreover, the reduction of V5+ to V4+ and even V3+ was identified as a crucial step in the reaction.A reaction scheme has been proposed based on catalytic experiments and spectroscopic insights.

Insights into biomass mild gasification based on mass-energy balance: Establishing condition, thermodynamic mechanisms, and product properties

To alleviate the challenge of gas and char quality competition arising from over oxidation during the biomass gasification. A new concept of biomass mild gasification based on mass and energy balance was proposed, wherein the energy produced during the oxidation stage precisely equals the energy consumed in the pyrolysis and reduction stages. An energy balance index (EBI), obtained through the combined use of TG-DSC-MS-FTIR and Gaussian model fitting to represent the relationship between mass loss and endothermic/exothermic properties among different reaction stages, was optimized by response surface methodology (RSM) to obtain the critical conditions of biomass mild gasification. Under two typical mild gasification conditions, the quality characteristics of mild gasification biochar were analyzed and the gas evolution characteristics and sequence were determined through the combination of two-dimensional correlation spectroscopy (2D COS). The results indicated that mild gasification can be achieved within a heating rate range of 21 °C/min to 26 °C/min, with the oxidation temperature ranging from 776 °C to 869 °C. Under mild gasification conditions, the biochar produced at 850 °C-20 °C/min had higher COOH content, which can regulate soil pH, promote organic matter degradation, and enhance biological activity. Under the 800 °C-25 °C/min mild gasification condition, more CO and CH4 were generated during the pyrolysis stage, but slightly more CO2 was also produced during both the pyrolysis and oxidation stages. This work provides comprehensive thinking on the precious control of gasification process, which lays a foundation for co-generation of high-quality char and gas.

Effects of WO3 and MoO3 loadings on vanadia-based catalysts for NH3-SCR: Revealed by in situ infrared and two-dimensional correlation spectroscopy

Vanadia-based catalysts have been widely applied in NOx reduction, while the promoting effects of WO3 and MoO3 are still under debate. Herein, we prepared V2O5/TiO2, V2O5-WO3/TiO2, and V2O5-MoO3/TiO2 catalysts and revealed that WO3 and MoO3 enhanced the activity of V2O5/TiO2, especially under wet conditions. In situ DRIFTS, two-dimensional correlation spectroscopy (2D COS), and DFT calculations demonstrated that NH3 adsorbed on Lewis acid sites of V2O5/TiO2, resulting in the formation of NH3ads-L1 (1284 cm−1, Ti sites of O=V–O–Ti) and NH3ads-L2 (1604 cm−1, V=O sites). By using 2D COS, we found that the NH3ads-L1 exhibited higher reactivity towards NO to produce NH2NO* via NH2*, which was promoted by WO3. Moreover, WO3 and MoO3 doping inhibited H2O adsorption, and promoted its desorption by increasing temperature, thus protecting the V=O sites on V2O5/TiO2. Also, 2D COS provided a new perspective for in-depth understanding of the active sites and intermediates in the NH3-SCR reaction.

Melt crystallization and thermal degradation profile of the antichagasic drug nifurtimox

Despite nifurtimox (NFX) being a traditional drug for treating Chagas disease, some of its physicochemical properties are still unknown, especially its thermal behavior, which brings important outcomes regarding stability and compatibility. In this work, a comprehensive study of NFX’s thermal properties was conducted to assist incremental innovations that can improve the efficacy of this drug in novel pharmaceutical products. For this purpose, thermal analyses associated with spectroscopy and spectrometry techniques were used. DSC analyses revealed that the melt crystallization of the NFX led to its amorphous form with the possible formation of a minor fraction of a different crystalline phase. Coats-Redfern method using TGA results indicated the activation energy of NFX non-isothermal degradation as 348.8 ± 8.2 kJ mol−1, which coincides with the C-NO2 bond dissociation energy of the 2-nitrofuran. Investigation of the isothermal degradation kinetics using FTIR 2D COS showed the possible detachment of radical NO2 and ethylene from the NFX structure, which could affect its mechanism of action. A preliminary mechanism for the thermal degradation of this drug was also proposed. The results enhanced the understanding of NFX's thermal properties, providing valuable insights, especially for developing NFX-based pharmaceutical products that involve thermal processing.

2D gradient and correlation FTIR analyses for optimizing thermal curing process of commercial-grade polyurethane coatings for automotive interior parts

Soft-feel coatings for automotive interior parts are a crucial factor in consumer purchase preferences owing to the growing awareness of human sensibility ergonomics. Herein, the thermal curing of commercial-grade polyurethane (PU) coatings was optimized using advanced spectroscopic tools. Conventional FTIR spectra were collected at various curing temperatures and times, and analyzed using two-dimensional (2D) gradient maps and 2D correlation spectroscopy (2D COS); while the former demonstrates the spectral variation trend with curing time, the latter provides whole spectral sequences that inform the cure reaction mechanism. The thermal curing continued for 50 min at 60 and 70 °C, and was halted after 30 min above 80 °C. According to the 2D COS and kinetic model fitting, the cure reaction was initiated by solvent evaporation and followed nucleation and growth mechanisms. PUs cured at lower temperatures were ductile owing to incomplete reactions, whereas PUs cured above 80 °C exhibited brittle features. Consequently, the optimal curing process was determined to be at 80 °C for 30 min. The 2D FTIR analytic tools can be useful in the development of high-quality soft-feel coatings for automotive interior parts.

Hierarchical zeolites TNU-9 and IM-5 as the catalysts for cracking processes

The 10-ring zeolites TNU-9 and IM-5 were obtained by a desilication and evaluated in series of acid-catalysed cracking reactions. n-Decane and 1,3,5-tri-iso-propylbenzene cracking were performed as model reactions, while vacuum gas oil, polypropylene and polyethylene were cracked into add-value lower molecular weight chemicals. The catalytic performance improvement of hierarchical zeolites was rationalized by deep acid sites characterization in situ FT-IR studies of pyridine, carbon monoxide and 2,6-di-tert-butylpyridine sorption. Further, operando FT-IR-GC studies supported by 2D COS (two-dimensional correlation) analysis provided insight into cracking and coking of catalysts during polypropylene and polyethylene decomposition. It was found that NaOH-derived catalysts ensure the most upsurged acidity, in terms of number and accessibility of the sites, and then with better performance. In VGO cracking the connected mesopores added post-synthesis increased yields to propylene and middle distillates and lowered coke production. A bigger share of iso-olefins was observed both in VGO and polyolefins cracking products.

Guanine adsorption on gold electrodes studied by in situ surface-enhanced infrared reflection absorption spectroscopy

The adsorption of guanine on single-crystal and thin-film gold electrodes has been explored by combination of cyclic voltammetry and ATR-SEIRA ‘in situ’ spectroscopy at two pD values (8 and 11.6) employing D2O as a solvent. The experimental conditions are selected to study the adsorption / desorption of the two forms of guanine involved in the second acid-base equilibria and its tautomeric forms.The ATR-SEIRA spectra of adsorbed guanine were compared to the absorption FT-IR spectra in solution and interpreted in light of DFT calculations of the different acid-base and tautomeric forms with different solvation states of the CO group. Furthermore, the preponderance of each tautomeric form and the possible changes in orientation with the electric field have been determined by analyzing the two-dimensional correlation spectrum (2D COS) as well as the influence of the potential on the integrated intensities of the spectral signals in the 1800–1400 cm−1 region. It has been found that at pD 8 the adsorbed keto-amino tautomer of neutral guanine predominates in solution and in adsorbed state, and adsorbed guanine slightly rotate its molecular plane with the potential. At pD 11.6 the keto-amino tautomer of anionic guanine is the unique form detectable in the solution, while in adsorbed state the keto-imino tautomeric form is also present with its preponderance increasing with the electrode potential.

Adsorption and Photo-Degradation of Organophosphates on Sulfate-Terminated Anatase TiO2 Nanoparticles

The adsorption and photocatalytic degradation of trimethyl phosphate (TMP) and triethyl phosphate (TEP), two environmentally relevant model pollutants, have been studied on commercial anatase TiO2 and sulfate-terminated anatase TiO2 nanoparticles by means of operando diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and 2D correlation spectroscopy (2D COS). It is concluded that both TMP and TEP adsorb dissociatively on anatase TiO2, while on the sulfate-terminated anatase TiO2, TMP and TEP adsorb associatively. Upon UV illumination, TMP and TEP are completely oxidized on sulfate-terminated anatase TiO2, as evidenced by the evolution of the IR bands characteristic for water and carbon dioxide. In contrast, on anatase TiO2, UV illumination leads to the formation of stable surface-coordinated carboxylate products, which impedes complete oxidation. 2D COS analysis suggests that parallel reaction pathways occur during oxidation under UV illumination, viz. methoxide/ethoxide (ads) → carboxylates (ads) and methoxide/ethoxide (ads) → aldehydes (ads) → carboxylates (ads). A parallel reaction occurs on sulfated TiO2 that yields CO2 and H2O by direct radical reactions with the methoxide groups with little, or no, formation of surface-coordinated intermediates. Sulfated TiO2 favor the formation of aldehyde intermediates, with reaction rates 10 times and 30 times faster for TMP and TEM, respectively, compared with commercial anatase TiO2. About 37% (33%) and 32% (24%) of TMP (TEP) were degraded on sulfated-terminated TiO2 and pure TiO2, respectively, after the first 9 min of UV illumination. We show that the sulfate-functionalization of TiO2 has two main functions. First, it prevents the formation of strongly bonded bridging carboxylates, thereby alleviating deactivation. Second, it promotes full oxidation of the organic side-chains into carbon dioxide and water. Improved electron-hole separation by the electrophilic S(VI) in combination with the blocking of bridging reaction intermediates is proposed to contribute to the improved activity. The presented results give insights into how acidic surface modifications change adsorbate surface chemistries, which can be used to increase the sustained activity of low-temperature photocatalysts.

Insight into the evolution characteristics on molecular weight of compost dissolved organic matters using high-performance size exclusion chromatography combined with a two-dimensional correlation analysis.

The information on molecular weight (MW) characteristics of DOM and relevant evolution behaviors during composting are limited. In this study, DOM extracted from co-composting of chicken manure and rice husks were comprehensively analyzed by using high-performance size exclusion chromatography (HPSEC) combined with a two-dimensional correlation spectroscopy (2D COS) to explore the evolution characteristics of MW of compost DOM. The HPSEC detected at UV of 254nm and at fluorescence (FL) Ex/Em wavelengths (315/410, 270/455nm) all showed a gradual increase in both weight-average and number-average MW for DOM, suggesting that the large MW fractions were continuously generated and polymerized during composting. The 2D COS applied on HPSEC-UV and -FL further identified the key active MW chromophoric (i.e., 0.5, 7.2. 9.5, 26.3, 30.7, and 83.9kDa) and fluorophoric (i.e., 0.55 and 3.5kDa) molecules that mainly participated in the transformation processes of compost DOM. Moreover, these active MW species were preferentially formed by the order of small to large molecules. A hetero-2D COS analysis disclosed the change sequence in the order of 0.5 and 7.2kDa chromophores → 3.5kDa fluorophores, and the 0.55 and 3.5kDa fluorophores → 26.3 and 83.9kDa chromophores.

Mechanistic stages of the SCR reaction – Insights into the trade-off between NO reduction and NH3 oxidation over CuSSZ-13 catalysts via isotopic 15NH3 and 18O2 TPSR and steady state studies supported by IR 2D COS and DFT modeling

Isotopic labeling investigations into SCR reaction were performed over CuSSZ-13 zeolites, obtained by one-pot synthesis or impregnation, and characterized by XRD, HR-SEM, TEM/EDX, EPR, and IR techniques. The course of SCR and internal ammonia oxidation (i-AMO) was revealed by isotopic TPSR and steady-state investigations using 15NH3 and 18O2 joined with IR Rapid Scan 2D-COS spectroscopy. The 14N15N and 15N2 profiles allowed for quantification of the relative contributions of the concurrent SCR and i-AMO reactions. Interpretation of the results was ascertained by DFT and first-principles thermodynamic modeling. Three temperature regions of SCR reactions, corresponding to NH3-rich, lean and dry conditions, were distinguished, and the main processes and intermediates involved in each stage were identified. For the conceptualization of SCR, a 2D diagram of the reactants and intermediates stoichiometry, oxidation state, and charge commensurability was constructed, and used for rationalization of the reaction mechanism.

Rapid effectual entrapment of pesticide pollutant by phosphorus-doped biochar: Effects and response sequence of functional groups

The purpose of this study is to clarify the mechanism of P-doped biochar adsorbing pesticide pollutants such as 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. Through environmental interference, adsorption isotherms and kinetic experiments, the mechanism evolution of 2,4-D adsorption by the inherent structure of biochar and the species difference of phosphorus-oxygen groups was investigated. Under controlled nitrogen flow, among the P-doped biochar produced at different pyrolysis temperatures (300, 500 and 700℃), the P-doped biochar produced at 700℃ (PBC-700) showed the best 2,4-D adsorption capacity (146.41 mg g−1). The adsorption of 2,4-D largely depends on the characteristic surface functional groups, specific surface area and porosity of biochar. In the adsorption process, hydrogen bonding and π-π EDA interaction dominate, and electrostatic force and pore filling play an auxiliary role. The chemisorption function of PBC-700 was weaker than that of PBC-300. The density functional theory (DFT) calculation results showed that the incorporation of P species regulated the electronic structure and surface charge distribution of the biochar. The two-dimensional correlation spectroscopy (2D COS) analysis revealed the order of the main functional groups involved in the adsorption process. Furthermore, the good recovery capacity improved the feasibility of P-doped biochar to repair surface water polluted by pesticides such as 2,4-D.

Investigating the Evolution of Structural Characteristics of Humic Acid Generated during the Continuous Anaerobic Digestion and Its Potential for Chromium Adsorption and Reduction

Humic acid (HA), as an important by-product, has been demonstrated to affect anaerobic digestion performance and subsequent land application of digestate via the batch anaerobic digestion process. However, the knowledge about the evolution of structure and function of HA during continuous anaerobic digestion (AD) is still unclear. Therefore, the current study examined the structural changes in HA produced during the continuous AD process and its metal-adsorption-reduction abilities. The results of three-dimensional fluorescence spectroscopy showed a general upsurge in humic-like components’ abundance (70–77%), with an increase in humification index (2.56–3.43). Likewise, the content of HA increased from 4.8 g L−1 to 6.9 g L−1 in the continuous AD process. The evolution of C-H, O-H, C=O, C=C, and C-O functional groups of HA was observed via the 2D COS FTIR analysis. Moreover, the concurrent dynamics of functional groups contributed to the higher adsorption (255.2 mg g−1) of Cr (VI) and reduction (60.3 mg g−1) of Cr (VI) to Cr (III) after 168 days of the continuous AD process. The findings of the current study not only advanced understanding of the evolution of HA during continuous anaerobic digestion and its metal remediation potential but also support further research toward developing an eco-friendly and innovative strategy for the remediation of heavy metals contaminated soils employing anaerobic digestate as an auxiliary agent.

Modulation of ODH Propane Selectivity by Zeolite Support Desilication: Vanadium Species Anchored to Al-Rich Shell as Crucial Active Sites.

The commercially available zeolite HY and its desilicated analogue were subjected to a classical wet impregnation procedure with NH4VO3 to produce catalysts differentiated in acidic and redox properties. Various spectroscopic techniques (in situ probe molecules adsorption and time-resolved propane transformation FT-IR studies, XAS, 51V MAS NMR, and 2D COS UV-vis) were employed to study speciation, local coordination, and reducibility of the vanadium species introduced into the hierarchical faujasite zeolite. The acid-based redox properties of V centres were linked to catalytic activity in the oxidative dehydrogenation of propane. The modification of zeolite via caustic treatment is an effective method of adjusting its basicity—a parameter that plays an important role in the ODH process. The developed mesopore surface ensured the attachment of vanadium species to silanol groups and formation of isolated (SiO)2(HO)V=O and (SiO)3V=O sites or polymeric, highly dispersed forms located in the zeolite micropores. The higher basicity of HYdeSi, due to the presence of the Al-rich shell, aided the activation of the C−H bond leading to a higher selectivity to propene. Its polymerisation and coke formation were inhibited by the lower acid strength of the protonic sites in desilicated zeolite. The Al-rich shell was also beneficial for anchoring V species and thus their reducibility. The operando UV-vis experiments revealed higher reactivity of the bridging oxygens V-O-V over the oxo-group V=O. The (SiO)3V=O species were found to be ineffective in propane oxidation when temperature does not exceed 400 °C.

Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance.

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm-2 and a Tafel slope of 65.6 mV dec-1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO2. For the mechanistic investigation, the lowest charge transfer resistance (Rct) and the highest double-layer capacitance (Cdl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H2O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm-2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.

2D COS and PCMW2D analysis of the magnetic transitions in Raman spectra of BiFeO3

BiFeO3 is one of the most attracting materials because it is the only known room-temperature multiferroic material. It has been studied by Raman spectroscopy extensively. We perform two-dimensional correlation spectroscopy (2D COS) and perturbation-correlation moving window two-dimensional correlation spectroscopy (PCMW2D) analysis on the temperature-dependent Raman spectra of a BiFeO3 single crystal. The two low temperature spin reorientation transitions around 135 K and 190 K are confirmed through the significant change in phonon peaks from PCMW2D correlation spectra. We also identify the origin of the mode at ~ 1255 cm−1, which has been controversial until now. In our 2D COS analysis, the intensity of this mode has a strong correlation with the intensity of 145 and 176 cm−1 phonons which correspond to the vibration modes of the Bi-O and Fe-O chemical bonds. We propose that the mode at ~ 1255 cm−1 is the two-phonon scattering of the 551 cm−1 mode assisted by the 145 −176 cm−1 phonons.

Investigation into the impact of aged microplastics on oil behavior in shoreline environments

Understanding the interactions between oil and other particles in shoreline can help determine the environmental risk and cleanup strategy after oil spill. Nevertheless, far less has been known regarding the impact of aged MPs on oil behavior in the shoreline environment. In this study, the aging course of polyethylene (PE) in shaking seawater and ultraviolet (UV) radiation conditions was investigated. The seawater aging mainly affected the physical properties of MPs, increasing its surface pores and hydrophilicity. UV aging significantly affected both the physical and chemical properties of MPs, which increased its hydrophilicity and crystallinity, decreased its mean particle size and introduced oxygen-containing functional groups onto MPs. The two-dimensional correlation spectroscopy (2D COS) analysis confirmed the evolution of oxygen-containing functional groups from C–O to CO. The effects of aged MPs on oil behavior in water-sand system were further explored. The oil remaining percentages were non-linearly changed with the increasing aging degree of MPs. The particle size of the aqueous phase after washing was inversely related to the oil remaining percentage. Further FTIR analysis revealed that C–O and C–H functional groups played an important role in the process of oil adsorbed on MPs.

Effects on the complexation of heavy metals onto biochar-derived WEOM extracted from low-temperature pyrolysis

Biochar-derived water-extractable organic matter (WEOM) was obtained under low-temperature pyrolysis (300 °C) using corncob as raw material. WEOM may affect the mobility and bioavailability of soil heavy metals (HMs) through complexation when biochar was used for soil HM remediation. Herein, the characteristics of complexation between HMs (Cr(III) and Cu(II)) and biochar-derived WEOM were investigated by using spectroscopic techniques in conjunction with parallel factor (PARAFAC) analysis and two-dimensional correlation spectroscopy (2D–COS). Six components were identified by PARAFAC modeling, in which protein-, fulvic- and humic-like components accounted for 48.86%, 25.63% and 25.51%, respectively. A nonlinear model was employed to determine the conditional stability constant (KM) and total ligand concentration (CL) of WEOM-HM complexes. The log KM values were in the range of 4.02–5.04 for WEOM-Cr(III) and 4.04–6.58 for WEOM-Cu(II). The 2D–COS in conjunction with log-transformed synchronous fluorescence spectroscopy (SFS) suggested that WEOM components were preferentially complexed with HMs in the following order: 433/270, 433/335, 496/270, 496/335, 370/335, 433/402, 496/402, 335/290, 402/290 for Cr(III), and 290/280, 390/280, 433/280, 496/280, 433/335, 496/335, 390/335, 433/420, 496/402, 335/290, 316/290 for Cu(II). The results of 2D–FTIR–COS suggested a preferential bonding of Cr(III) to the C–N group of alkyl, and Cu(II) to the CO group of alcohols, ethers and esters. Meanwhile, the CO group of ethers and the CN group of alkyl indicated preferential susceptibilities for the addition of Cr(III) and Cu(II) at different concentrations. In addition, protein-like components had remarkably higher total ligand concentration (CL) than fulvic- or humic-like components.

Mixing dynamics of diethyl ether and chloroform

Mixing dynamics of liquid diethyl ether and chloroform were studied by time-resolved Fourier-transform infrared absorption spectroscopy in attenuated total reflectance mode (ATR-FTIR). An in situ experiment where chemicals were mixing in the vertical cell directly attached to the diamond ATR accessory was carried out. The data were analyzed by two-dimensional correlation spectroscopy (2D COS) and multivariate curve resolution (MCR). The analysis of ATR-FTIR spectra has shown that each species (diethyl ether and chloroform) exist in an unbound (free) state and bound state (as a part of the molecular complex). The concentration and spectral profiles of mixture components were obtained using MCR decomposition. A theory of nonlinear diffusion has been used to model the experimentally obtained concentration profiles. It has been shown that the theoretical concentration profiles are in good qualitative agreement with experimental ones.