Metal-free Nitrogen-doped Carbon Research Articles

Effect of structure of metal-free nitrogen-doped coal-based carbon on catalytic oxygen reduction

In carbon-based oxygen reduction reaction (ORR) catalysts, metal-free nitrogen-doped carbon-based materials generally have higher catalytic stability compared to metal catalysts with reduced catalytic activity due to the occurrence of metal agglomeration during the catalytic reaction. In this paper, a metal-free nitrogen-doped carbon-based ORR catalyst NCOH5-900 with a half-wave potential of 0.846 V and onset potential of 0.94 V was prepared using coal as the carbon source, dicyandiamide as the nitrogen source and KOH as the activator. The material has good ORR catalytic performance with half-wave potential and onset potential comparable to Pt/C catalyst with the same mass loading, with better resistance to methanol toxicity and catalytic stability. The physical and chemical properties of the prepared catalyst were controlled by adjusting the amount of nitrogen doping and activation temperature to establish the relationship between the material structure and the ORR performance. The results suggest that for the metal-free nitrogen-doped carbon-based material, the good ORR catalytic performance is attributed to the abundant edge defects, high graphitization, good mixed structure of micro/mesopores, large nitrogen content, and high ratio of pyridine to graphitic nitrogen. Finally, the catalytic mechanism of NCOH5-900 for ORR is investigated using in-situ attenuated total reflection Fourier infrared (ATR-FTIR) and in-situ Raman, confirming the four-electron reduction process of O2 via a continuous dual step of two-electron transfer process.

Metal-Free Nitrogen-Doped Mesoporous Carbons for the Mild and Selective Synthesis of Pyrroles from Nitroarenes via Cascade Reaction.

The cascade synthesis of pyrroles from nitroarenes is an attractive alternative strategy. However, metal catalysts and relatively high temperatures cover the existing reported catalytic systems for this strategy. The development of nonmetallic heterogeneous catalytic systems for the one-pot synthesis of pyrrole from nitroarenes under mild conditions is both worthwhile and challenging. Herein, we describe an exceptionally efficient method for the synthesis of N-substituted pyrroles by the reductive coupling of nitroarenes and diketones over heterogeneous metal-free catalysts under mild conditions. Nonmetallic NC-X catalysts with high activity were prepared from the pyrolysis of well-defined ligands via simple sacrificing hard template methods. Hydrazine hydrate, formic acid, and molecular hydrogen can all be used as reducing agents in the hydrogenation/Paal-Knorr reaction sequence to efficiently synthesize various N-substituted pyrroles, including drugs and bioactive molecules. The catalytic system was featured with good tolerance to sensitive functional groups and no side reactions such as dehalogenation and aromatics hydrogenation. Hammett correlation studies have shown that the electron-donating substituents are beneficial for the one-pot synthesis of N-substituted pyrroles. The results established that the outstanding performance of the catalyst is mainly attributed to the contribution of graphitic N in the catalyst as well as the promotion effect of the mesoporous structure on the reaction.

Efficient PMS activation toward degradation of bisphenol A by metal-free nitrogen-doped hollow carbon spheres

Peroxymonosulfate (PMS) activation methods conventionally face challenges such as high energy consumption and the risk of metal leaching, limiting their practical application. Metal-free catalysts often face the problem of low catalytic activity. This study designed an in-situ nitrogen-doped hollow carbon catalyst (DNC-9), which offers balances efficient catalytic performance and metal-free catalysis. The results indicate that the DNC-9/PMS system effectively degrades bisphenol A, achieving complete degradation over a broad pH range (3.0–9.0). Through structure modification, the degradation efficiency of bisphenol A compared with SiO2@DNC-9/PMS system was improved by around 6 times and the degradation kinetic rate can reach 0.346 min−1. DNC-9 can activate PMS, resulting in a higher concentration of singlet oxygen without the generation of free radicals. Graphitic nitrogen in DNC-9 plays a crucial role in this activation, offering adsorption sites that facilitate decomposition of PMS and generating 1O2. In addition, graphitic nitrogen forms a transient active intermediate, DNC-9-PMS*, enhancing bisphenol A degradation. The catalyst recovers its high activity to complete bisphenol A removal with 15 min after thermal regeneration in cyclic experiments, demonstrating its potential as a practical solution for the efficient degradation of emerging contaminants.

Temperature-Dependent Investigation of ORR Kinetics on Non-Precious Metal-Free Catalysts in Alkaline Media - Doping Effect on Electrocatalysis

The kinetic analysis of oxygen reduction reaction (ORR) on non-precious catalysts is cumbersome due to the formation of more than one major products ( and ). In the present study, ORR is investigated on Vulcan XC-72 (C) and a metal-free nitrogen-doped (~≤ 1%) carbon (N/C-900) catalysts in 0.1 M KOH [1]. The experiments are conducted in the temperature range of 293–323 K using a rotating ring disk electrode (RRDE) assembly to quantify the product distribution, viz., and . The measured kinetic current () is partitioned into and on the basis of the potential-dependent product distribution ( and ) .and is used in the estimation of kinetic parameters [2]. The α values are derived from Butler-Volmer (B-V) theory, Tafel equation at high overpotentials (η), and from the derivative of the change in Gibbs free energy of activation () with respect to η. The α values obtained from all the three methods are different. Therefore, the origin of the difference in the α values is the subject of the present investigation. The seemingly unreasonable values of (> 1.0)on N/C-900 may be due to the alternative lower energy path for the formation of activated complex along with the change in the free energy of the reactant [3,4]. On C, it does not provide any alternative pathway for the formation of activated complex and perhaps η influences only the energy state of the reactant. Therefore, the free energy of activation for the formation of activated complex is a stronger function of η on N/C-900 and an indication of strong electrocatalysis. References B. Bera, T. Kar, A. Chakraborty, M. Neergat, J. Electroanal. Chem., 805, 184–192 (2017).R. Das, D. Choudhury, R. Maurya, S. Sharma, M. Neergat, Langmuir,39 (12), 4351–4361 (2023).U. Stimming, J. Wang, A. Bund, ChemPhysChem, 20 (22), 3004–3009 (2019).R. Maurya, R. Das, A. K. Tripathi, M. Neergat, Phys. Chem. Chem. Phys., 25, 700–707 (2023). *Corresponding author: Tel.: +91 22 2576 7893; Fax: +91 22 2576 4890E-mail: nmanoj@iitb.ac.in (M. Neergat)

Metal-Free Nitrogen-Doped Porous Carbons for Nitriles and Amides Synthesis from 1,2-Diols via Oxidative Cleavage of C–C Bonds

Metal-Free Nitrogen-Doped Porous Carbons for Nitriles and Amides Synthesis from 1,2-Diols via Oxidative Cleavage of C–C Bonds

Synthesis of metal-free nitrogen-doped mesoporous carbon nanosheets with reference to molecular self-assembly for efficient peroxymonosulfate activation

The application of metal-free carbon materials in Sulfate radical-based advanced oxidation processes (SR-AOPs) has attracted great attention. In SR-AOPs, porosity and active sites are the keys for nitrogen-doped carbon materials to exhibit high catalytic activity. In this paper, melamine and gallic acid were selected as raw materials, preparing metal-free nitrogen-doped carbon materials by using the molecular self-assembly synthesis method. The catalysts with different structural morphology and surface chemistry were obtained by controlling the pyrolysis temperature. It proposed the formation mechanism of nitrogen-doped mesoporous carbon nanosheets (NMC). The pyrolysis temperature was critical for the regulation of surface properties as well as the structure of carbon materials. It was found that NMC-800 exhibited fluffy and porous microstructure, and various active sites on the surface of the catalyst, including graphite N, pyridine N and CO. In the NMC-800/PMS system, the SMX degradation efficiency and corresponding rate constant could achieve 90.3 % and 0.1705 min−1, respectively. Besides, the degradation pathways and intermediate products of SMX were discussed by the analysis of quenching experiments, electron spin resonance (ESR) and liquid chromatography-mass spectrometry (LC-MS).

Locking nitrogen dopants in porous carbons through in situ grafting strategy for enhanced oxygen reduction reactions

We report here the synthesis of N-doped porous carbon (PC) through a convenient melamine pre-grafting strategy. The melamine derivative with a monolayer structure was first grafted on the surface of the micropores of PC using a suitable diazotization reaction of melamine in an aqueous solution. After pyrolysis, PC grafting with melamine derivative was converted to the obtained N-doped PC. Meanwhile, more nitrogen dopants were grafted, and nitrogen functionalities were reconstructed to generate more graphitic N and pyridinic N atoms, in which the mesopores volume was consequently enlarged. Because of the unique structures mentioned above, the as-obtained N-doped PC exhibited enhanced oxygen reduction activity under alkaline compared with the N-doped PC from the standard physical mixture of PC and melamine. Besides, the obtained N-doped PC showed a comparable half-wave potential, remarkable durability, and good methanol tolerance compared with the commercial 20% Pt/C electrocatalyst. The results presented here could guide the development of new and improving metal-free nitrogen-doped porous carbon catalysts toward oxygen reduction reaction.

Metal-free nitrogen-doped carbon nanodots as an artificial nanozyme for enhanced antibacterial activity

Bacterial infections have become a considerable obstacle to public health due to the emergence of antibiotic resistance. Herein, we rationally developed a novel and attractive nitrogen-doped carbon nanodots (N-CNDs) as efficient metal-free artificial nanozymes that synergistically and efficiently inhibit bacterial survival by inheriting the bacteriostatic ability of tea polyphenols and light-triggered oxidase-like catalytic activity. The excellent oxidase-mimicking activity exhibited by N-CNDs in the light was mediated by superoxide radicals (•O2−) with a high maximum reaction rate (1.59 μM⋅s−1) and a low Michaelis constant (0.421 mM). Furthermore, the constructed N-CNDs-based nanozyme was demonstrated to serve as a complex biomaterial platform for efficient sterilization by light-driven oxygen molecule generation of •O2−. Remarkably, the inherent antibacterial ability of N-CNDs can effectively inhibit both Gram-positive and Gram-negative bacteria, particularly against Gram-positive S. aureus at a minimum inhibitory concentration (MIC90) of 375 μg⋅mL−1. The inactivation rates of N-CNDs alone agsinst E. coli and S. aureus were 59.72% and 37.15%, respectively. However, the inactivation rates of E. coli and S. aureus by N-CNDs achieved by light were as high as 97.91% and 80.02%, respectively. Encouragingly, a two-way ANOVA revealed that the concentration of N-CNDs and the duration of light exposure had a synergistic effect on antibacterial behavior, which provided favorable conditions for the sustained eradication of exposed bacteria. This synergistic strategy for bacterial eradication based on a novel metal-free carbon-based nanozyme provides a powerful and feasible approach for bacterial contamination management in food safety and environmental protection.

The origin of selective nitrate-to-ammonia electroreduction on metal-free nitrogen-doped carbon aerogel catalysts

Electrocatalytic nitrate reduction reaction (NitRR) to NH3 provides an appealing route to reform the energy-consuming ammonia industry. Considerable studies have demonstrated transition-metal-based catalysts for the NitRR, while most of them suffer from high cost, poor stability, and unsatisfactory selectivity. In this work, a group of carbon-based aerogel catalysts with regulated N species have been developed for highly efficient nitrate-to-ammonia reduction. The results show that the electrocatalytic performance is dependent on the graphitic-N moiety, where the catalyst with the highest content of graphitic-N moiety exhibits a maximum NH3 yield rate of 1.33 mgNH3 h−1 cm−2 with the faradaic efficiency of ca. 95%. The theoretical investigation further reveals the strong adsorption of nitrate on graphitic-N moiety as the reason for the enhanced NO3ˉ-to-NH3 activity. This study, thus, provides a fundamental understanding of the intrinsic mechanism of the NitRR on nitrogen-doped carbon structures, facilitating the rational design of metal-free catalysts for advanced electrosynthesis.

Self-Templated Conversion of a Self-Healing Metallogel into an Active Carbon Quasiaerogel: Boosting Photocatalytic CO2 Reduction by Water

Healing and photosynthesis are two prime examples of intrinsic aptitude in the incredibly diverse plant kingdom. Inspired by nature, the development of new materials with the intrinsic ability of healing and artificial photosynthesis is of current interest. In this regard, herein, a new waterborne self-healing metallogel (Nd-SHMG) along with a self-templated carbonization strategy is presented for the synthesis of a neodymium@nitrogen-doped carbon quasiaerogel (Nd@NCA) catalyst. The stiffness of the metallogel (self-healing, self-sustaining, and molding behavior) can be controlled by tuning the synthetic conditions. A metal-free nitrogen-doped carbon quasiaerogel (MF@NCA) was also prepared via partial removal of the metal from the Nd@NCA catalyst. The as-synthesized Nd@NCA and MF@NCA catalysts were composed of highly porous 2D sheets which are grown on top of each other, adopting a 3D foam-type structure. The porosity (∼9 fold) and the CO2 adsorption capacity (∼8 fold) can be gradually increased ‘on demand’ by partial removal of the metal ion from the pristine Nd@NCA. The as-synthesized catalysts exhibit excellent photocatalytic activity for CO2 conversion into CO (∼17–24 μmol g–1) with over ∼87% selectivity without adding sacrificial agents. Isotopic carbon-labeled (13CO2) in situ diffuse reflectance infrared Fourier transform spectroscopy analysis was performed, and a plausible mechanism was outlined for photocatalytic CO2 reduction to CO. With this work, we introduce a facial and feasible strategy to prepare a Nd-SHMG and their conversion into active bifunctional carbon quasiaerogel-based catalysts, which can adsorb and convert CO2 selectively into CO without adding sacrificial agents in the presence of water and light.

Metal-free nitrogen-doped porous carbon nanofiber catalyst for solar-Fenton-like system: Efficient, reusable and active catalyst over a wide range of pH

Water pollution is a growing environmental crisis caused by industrialization. In-situ production of reactive oxygen species (ROS) is one of the most promising strategies to challenge this problem. However, developing a robust and efficient catalyst that can operate in harsh conditions without generating secondary pollution and tackle the recycling difficulties of powder catalysts remains a challenge. In this study, a graphitized N-doped carbon nanofiber (CNF) catalyst was synthesized in a direct synthesis approach, which is more efficient in time and cost and suitable for industrial applications, by means of electrospinning and carbonization process. Zinc acetate and iron nitrate functioned as a template for porous structure generation and carbon graphitizing catalysts. The as-synthesized catalyst was used in the wide pH range. This was mainly due to: i) the high surface area (∼ 652 m2 g−1) and the micro-mesoporous structure, which have reduced the inner diffusion resistance and facilitated mass transport radically during the reaction. ii) The enhanced electron transfer kinetics through the long 1D CNF revealed by the cyclic voltammetry analysis. iii) The abundance of oxygen-containing function groups, graphitic-C pyridinic-N and graphitic-N active sites that facilitated the activation of H2O2 and the generation of the ROS responsible for the degradation of the organic pollutants. The catalysts’ 1D structure and lightweight enabled the catalyst recovery and reuse.

Metal-Free N-Doped Carbons for Solvent-Less CO2 Fixation Reactions: A Shrimp Shell Valorization Opportunity.

High anthropogenic CO2 emissions are among the main causes of climate change. Herein, we investigate the use of CO2 for the synthesis of organic cyclic carbonates on metal-free nitrogen-doped carbon catalysts obtained from chitosan, chitin, and shrimp shell wastes, both in batch and in continuous flow (CF). The catalysts were characterized by N2 physisorption, CO2-temperature-programmed desorption, X-ray photoelectron spectroscopy, scanning electron microscopy, and CNHS elemental analysis, and all reactivity tests were run in the absence of solvents. Under batch conditions, the catalyst obtained by calcination of chitin exhibited excellent performance in the conversion of epichlorohydrin (selected as a model epoxide), resulting in the corresponding cyclic carbonate with 96% selectivity at complete conversion, at 150 °C and 30 bar CO2, for 4 h. On the other hand, in a CF regime, a quantitative conversion and a carbonate selectivity >99% were achieved at 150 °C, by using the catalyst obtained from shrimp waste. Remarkably, the material displayed an outstanding stability over a reaction run time of 180 min. The robustness of the synthetized catalysts was confirmed by their good operational stability and reusability: ca. (75 ± 3)% of the initial conversion was achieved/retained by all systems, after six recycles. Also, additional batch experiments proved that the catalysts were successful on different terminal and internal epoxides.

Tailored defects for metal-free nitrogen-doped carbons toward efficient oxygen reduction reaction using tripolycyanamide-based microporous polymer as precursor

Fabrication of metal-free carbon electrocatalysts with low-cost, high-performance and outstanding stability is great important for realizing the widespread application of fuel cells and metal-air batteries. Herein, we report a simple approach for the preparation of N-doped and defects-rich metal-free carbon (NDC) catalysts via carbonization of tripolycyanamide-based microporous polymer (TCAMP) in O2/N2 atmosphere, where the N-rich TCAMP was synthesized by a simple two-step polymerization process using the low-cost tripolycyanamide monomer (TCA) and paraformaldehyde as monomer. Raman spectra and X-ray diffraction (XRD) characterization indicated that the defects in NDCs’ carbon skeleton increased with the increasing pyrolysis temperature. Electrochemical studies showed that NDCs pyrolyzed in O2/N2 atmosphere presented a higher efficient oxygen reduction reaction (ORR) activity than its counterpart pyrolyzed in Ar atmosphere. The NDCs obtained at the pyrolysis temperature of 900 °C (NDC-900) presented an impressive oxygen reduction reaction (ORR) activity with a high half-wave potential of 0.853 V, owing to its large surface area (1808 m2 g−1), hierarchical meso‑micro pores and high active sites from the synergistic effect of N-doping and defects. Moreover, as-synthesized NDC-900 displayed a much better stability and methanol tolerance than commercial Pt/C catalyst. This work thus gives insights into fabricating promising alternative carbon catalysts for ORR process via one-step pyrolysis process using low-cost raw material.

Electrochemical Generation of Catalytically Active Edge Sites in C2 N-Type Carbon Materials for Artificial Nitrogen Fixation.

The electrochemical nitrogen reduction reaction (NRR) to ammonia (NH3 ) is a potentially carbon-neutral and decentralized supplement to the established Haber-Bosch process. Catalytic activation of the highly stable dinitrogen molecules remains a great challenge. Especially metal-free nitrogen-doped carbon catalysts do not often reach the desired selectivity and ammonia production rates due to their low concentration of NRR active sites and possible instability of heteroatoms under electrochemical potential, which can even contribute to false positive results. In this context, the electrochemical activation of nitrogen-doped carbon electrocatalysts is an attractive, but not yet established method to create NRR catalytic sites. Herein, a metal-free C2 N material (HAT-700) is electrochemically etched prior to application in NRR to form active edge-sites originating from the removal of terminal nitrile groups. Resulting activated metal-free HAT-700-A shows remarkable catalytic activity in electrochemical nitrogen fixation with a maximum Faradaic efficiency of 11.4% and NH3 yield of 5.86µg mg-1 cat h-1 . Experimental results and theoretical calculations are combined, and it is proposed that carbon radicals formed during activation together with adjacent pyridinic nitrogen atoms play a crucial role in nitrogen adsorption and activation. The results demonstrate the possibility to create catalytically active sites on purpose by etching labile functional groups prior to NRR.

Synergetic effect of nitrogen-doped carbon catalysts for high-efficiency electrochemical CO2 reduction

The use of carbon-based materials is an appealing strategy to solve the issue of excessive CO2 emissions. In particular, metal-free nitrogen-doped carbon materials (mf-NCs) have the advantages of convenient synthesis, cost-effectiveness, and high conductivity and are ideal electrocatalysts for the CO2 reduction reaction (CO2RR). However, the unclear identification of the active N sites and the low intrinsic activity of mf-NCs hinder the further development of high-performance CO2RR electrocatalysts. Achieving precise control over the synthesis of mf-NC catalysts with well-defined active N-species sites is still challenging. To this end, we adopted a facile synthesis method to construct a set of mf-NCs as robust catalysts for CO2RR. The resulting best-performing catalyst obtained a Faradaic efficiency of CO of approximately 90% at −0.55 V (vs. reversible hydrogen electrode) and good stability. The electrocatalytic performance and in situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy measurements collectively revealed that graphitic and pyridinic N can synergistically adsorb CO2 and H2O and thus promote CO2 activation and protonation.

Synergetic Photo-Thermo Catalytic Hydrogen Production by Carbon Materials.

Photo-thermo catalytic hydrogen production represents one of the most promising routes for channeling solar energy but typically suffers from high reaction temperatures. In this work, we develop photo-thermo catalytic hydrogen production at low temperatures by cost-effective, nonplasmonic, and metal-free nitrogen-doped carbon materials (CNO1-x). We demonstrate that due to the photothermal conversion of CNO1-x, carrier generation is improved and electron migration is enhanced to suppress the recombination of electron-hole pairs, both of which promote hydrogen production by photocatalysis, while generated hydrogen radicals facilitate the regeneration of active sites for hydrogen production by thermocatalysis. Such synergy greatly promotes photo-thermo catalytic hydrogen production at low temperatures. These results demonstrate the great promise of photo-thermo catalytic hydrogen production over carbon materials at low temperatures.

Metal-Free Nitrogen-Doped Porous Carbon Nanofiber Catalyst for Solar-Fenton-Like System: Efficient, Reusable and Active Catalyst Over a Wide Range of Ph

Metal-Free Nitrogen-Doped Porous Carbon Nanofiber Catalyst for Solar-Fenton-Like System: Efficient, Reusable and Active Catalyst Over a Wide Range of Ph

Regulable pyrrolic-N-doped carbon materials as an efficient electrocatalyst for selective O2 reduction to H2O2

Metal-free nitrogen-doped carbon catalysts with pyrrolic-N as the active site were efficiently synthesized via a direct carbonization method, which exibited a high two-electron oxygen reduction reaction performance.

Strategic combination of nitrogen-doped carbon quantum dots and g-C3N4: Efficient photocatalytic peroxydisulfate for the degradation of tetracycline hydrochloride and mechanism insight

• N-CQDs/g-C 3 N 4 /PDS photocatalytic system was firstly used for HTC degradation. • N-CQDs/g-C 3 N 4 efficiently activated PDS under visible-light irradiation. • Excellent charge separation efficiency can be obtained due to N-CQDs and PDS. • •SO 4 − , O 2 − and h + were found as the dominant contributors to the HTC degradation. • The mechanism of N-CQDs/g-C 3 N 4 /PDS photocatalytic system was proposed. Photo-assisted peroxydisulfate (PDS) activation has exhibited a great potential for pollution control. In this study, metal-free nitrogen-doped carbon quantum dots (N-CQDs) modified g-C 3 N 4 composite was fabricated and used to activate PDS under visible light to effectively remove tetracycline hydrochloride (HTC) in wastewater. Specifically, almost 90% of HTC (20 mg/L) was removed in 60 min under the conditions of an initial value of catalysis dose of 0.5 g/L and PDS dose of 0.6 g/L. Electron spin resonance analysis and trapping experiments confirmed that SO 4 − , O 2 − and h + were found as the dominant contributors to the HTC degradation. PDS and N-CQDs acted as an electron acceptor to transfer the photogenerated charges, resulting in the successful activation of PDS. The promoting visible light absorption can be ascribed to up-conversion effect of N-CQDs. The combination strategy provides an innovative approach to synthesize binary metal-free carbonaceous photocatalysts for implementing PDS-based oxidative degradation of pollutants.

Development of Stable CO2 Electro-Reduction Catalyst in Real Water Matrix

Artificial photosynthesis refers to the conversion of water and CO2 into value-added chemicals powered by sunlight, and is the holy grail of a sustainable carbon cycle of chemicals. Since a big challenge facing this system is the conversion of stable CO2 into the desired chemicals, most studies have focused on the development of high-performing catalysts within well-refined and restricted test environments. However, such superior performances cannot guarantee their feasibilities in realistic conditions for future commercialization or practical application unless their durability issues are secured. Here we report a one-step ahead approach to develop a more practical and advanced CO2 electro-reduction catalyst with essential clues to overcome the obstacles from realistic conditions, based on the understanding of CO2 reduction reaction deactivation phenomena. Our investigation firstly deals with the performance profile of an Ag electrode, selected as a standard catalyst for CO production, in real-life used tap water which is representative general purpose water. Screening and accompanying thorough analyses on various components in tap water ranging from alkali earth metals to transition/post-transition metals elucidated the types of impurities that can impede the catalytic activity by surface deposition, and consequentially cause the deactivation. Based on the findings involving Ag, a design strategy for a catalyst having excellent tolerance to the deactivation factors was suggested using a carbon-based material with heteroatom-doped active sites. A metal-free nitrogen-doped short carbon nanotube was prepared by a simple three-step process, and was denoted as ball mill N-CNT. As expected, the ball mill N-CNT showed a competitive and tolerant performance to the metal impurities regardless of the nature of the water sources, deionized water and tap water.