Remarkable adsorptive removal of nitrogen-containing compounds from hydrotreated fuel by molecularly imprinted poly-2-(1H-imidazol-2-yl)-4-phenol nanofibers

Molecularly imprinted polymer (MIP) nanofibers were prepared by the electrospinning of poly 2-(1H-imidazol-2-yl)-4-phenol (PIMH) in the presence of various nitrogen containing compounds (N-compounds). Molecularly imprinted polymer nanofibers show selectivity for various target model nitrogen-containing compounds with adsorption capacities of 11.7 ± 0.9 mg g−1, 11.9 ± 0.8 mg g−1 and 11.3 ± 1.1 mg g−1 for quinoline, pyrimidine and carbazole, respectively. Molecular modelling based upon density functional theory (DFT) indicated that hydrogen bond interactions may take place between the lone-pair nitrogen atom of model compounds (quinoline and pyrimidine) and the –OH and –NH groups of the PIMH nanofibers. The adsorption mode followed the Freundlich (multi-layered) adsorption isotherm, which indicated possible nitrogen–nitrogen compound interactions. Molecularly imprinted polymer nanofibers show potential for the removal of nitrogen-containing compounds in fuel.


Introduction
Fuel oil is the major source of energy for industrial machines and most vehicles in many countries of the world, and it is obtained mainly from fossil sources. 1 The hydrocarbons are mixed with variable quantities of sulfur-, nitrogen-, and oxygen-containing compounds. Renery feedstocks in general are extremely complicated chemical mixtures in which each heteroatom is present in the form of literally hundreds of different compounds. In general, the presence of organonitrogen compounds in fuel results in fuel instability during storage, due to the formation of gums, colours and sediments, compounds, such as quinoline and related molecules are capable of binding strongly on catalyst surfaces, hence, deactivating rening catalysts. [2][3][4][5][6][7] The most harmful effect of nitrogen compounds in fuel is the emission of NOx into the environment which is a major source of pollution that causes many environmental hazards like acid rain, greenhouse effect and photochemical smog.
New severe environmental regulations call for much lower levels of heteroatom-derived pollutants, organosulfur compounds and organosulfur compounds and this has stimulated an intensication of research and development efforts toward new or improved processes. 8 Due to the harm posed by these gases, the US EPA aimed at improving air quality mandated the reduction of nitrogen content in diesel fuel to ultra-low levels of <1 mg L À1 , 9 South Africa is also driving toward achieving the ultra-low levels.
Hydrodenitrogenation (HDN) is currently being employed to eliminate organonitrogen compounds in fuels. These extensively used technologies enabled oil reneries throughout the world for many years to systematically reach a ceiling of ca. 70% nitrogen removal, corresponding to a nal content of about 0.5 wt% N at typical operating conditions (25-50 atm, 330-350 C). [10][11][12][13] This indicated that the HDN technique is limited in eliminating organonitrogen compounds, thus requires alternative/complementary techniques such as extraction denitrogenation (EDN), oxidation denitrogenation (ODN), adsorptive denitrogenation (ADN), and biodenitrogenation are currently under study.
Extractive denitrogenation or liquid-liquid extraction is another method that has been applied in the removal of organonitrogen compounds in fuel. 14 This method suffers from the fact that other compounds can also be extracted along with the organonitrogen compounds. Oxidative denitrogenation (ODN), an alternative/complementary technique to the HDN, involves the oxidation of nitrogen-containing compounds to form oxygenated derivatives. Ishihara et al. 15 reported that nitrogen-containing compounds give N-oxide and other products due to cycle cleavage as well as polymer formation due to the presence of radicals. Ding et al., 16 recently reported the mild oxidation of pyrimidine to N-oxides with H 2 O 2 by vanadium-substituted polyoxometalate. However, the reaction did not proceed to the removal of the N-oxides. Recently, our research group 17 described a technological method for the removal of nitrogen compounds from fuels, via oxidation and extractive adsorption. Oxidative denitrogenation is an expensive technique which requires the development of additional plant in the rening industry.
Adsorptive denitrogenation (ADN) is about the most recent method that is being applied to remove organonitrogen compounds in fuel oil. So far, many adsorbents such as activated carbon, zeolites, silica, ion-exchange resins have been used for the ADN, [18][19][20][21] with less selectivity in the removal of organonitrogen compounds in fuels. However, sorbent materials such as molecularly imprinted polymers (MIPs) fabricated through imprinting of templates unto polymers suffice as potential adsorbents for the adsorption of these compounds. 22 Molecular imprinting of polymers is a technique employed for the introduction of recognition sites into polymeric matrices via the formation of bonds between the imprinting molecule (template) and functional groups within the polymer network. 22 Hence, the need to develop smart polymer nanober-based adsorbents [molecularly imprinted polymers (MIPs)] with large surface area-to-volume ratio for the selective removal of sulfonated compounds in fuels. 22 In this study, we describe the selective adsorption of organonitrogen compounds (quinoline, carbazole and pyrimidine) over molecularly imprinted poly 2-(1H-imidazol-2-yl)-phenol (PIMH) nanobers for the rst time by employing the solid phase extraction technique. A combined experimental and computational study was adopted to gain a fundamental understanding of the possible interactions responsible for adsorption. Complete diesel fuel analysis prior and aer adsorption was achieved through the use of LECO Pegasus GC Â GC-HRT.
Polymer solutions were respectively poured into a 25 mL syringe attached to a needle connected to the positive electrode of a high voltage power supply (Series EL, Glassman high voltage Inc). A syringe pump (Model NE-1010, New Era Pump Systems Inc. USA) was used to supply a constant ow of polymer solution from the syringe during the electrospinning process. A voltage of 20 kV was applied to the polymer solution which was pumped at a ow-rate of 0.3 mL h À1 , with a distance between the needle tip and aluminium collector plate placed at 15 cm. The repulsive electrical forces between charged nanobers enable them to spread smoothly and the solvent evaporates resulting in solidication while traveling toward the grounded collector. The template molecules (nitrogen containing compounds) imprinted within the nanobers were removed by washing the nanobers via Soxhlet extraction with a solution mixture of warm-to-hot methanol and acetonitrile (1 : 1) until no templates was detected on the GC.

Adsorption studies of model nitrogen containing compounds
Nitrogen compounds adsorption studies were performed under batch conditions by weighing a known mass of molecularly imprinted poly 2-(1H-imidazol-2-yl)-4-phenol nanobers (50 mg) into screw-capped vials containing 3 mL of nitrogen containing compounds (120 mg L À1 ) alongside other molecules. The screw-capped vials containing nitrogen compounds were le under mechanical agitation 100 rpm for 12 h. Progress in the adsorption of the various nitrogen containing compounds were followed by withdrawing aliquots for measurement aer every hour. Adsorption capacity, q e (mg g À1 ) was calculated from eqn (1).
where C o , C e , W and V are the initial concentration (mg L À1 ), equilibrium concentration (mg L À1 ), dry weight of nanobers (g) and solution volume (L) respectively. Conditioning of adsorbents was carried-out by pre-wetting adsorbents with solvents employed in dissolving the nitrogen compounds.

Solid phase extraction
Column preparation. One millilitre plastic syringes were used as column in the SPE manifold. A small amount of glass wool was placed at the bottom of each syringe to prevent loss of the molecularly imprinted nanobers during sample loading followed by introducing 50 mg of molecularly imprinted nanobers were loaded into the column. It was conditioned successively with hexane. Aer each use, the nanobers in the column was washed with large volumes of dichloromethane and methanol ($10 mL); and then stored for the next experiment. A typical solid phase extraction (SPE) manifold employed for the study is presented in Fig. S1. †

Pre-concentration
The molecularly imprinted nanobers column method was tested with model solutions prior to the selective adsorption and determination of N-compounds in fuel. For N-compound adsorption, 3 mL solution containing known amount of Ncompounds in model fuel was employed. The column was preconditioned by passing hexane solution under gravity. Aer passing of this solution ending, the column was loaded with Ncompounds solution. The adsorbed N-compounds on the column were eluted with 5-10 mL portion of methanol : acetonitrile (1 : 1). The eluent was analysed for the determinations of the various N-compound concentrations by GC-FID and GC Â GC-HRT.

Van't Hoff plot
The Van 't Hoff plot was used to determine the thermodynamic parameters such as enthalpy, entropy and Gibbs free energy of adsorption process. 24 Van 't Hoff experiments for all model organonitrogen compounds were carried out at 30, 35, 40 and 45 C by using batch adsorption process. Aliquots of analyte solutions are withdrawn at every 20 min interval and analysed by using a GC-FID. Thus, DH can be determined from the slope of the linear Van't Hoff plot i.e. in K ad versus (1/T). 24 Isothermal Titration Calorimetry (ITC) studies was also conducted and presented in the ESI (Section B). † Molecular interactions between poly 2-(1H-imidazol-2-yl)-4-phenol (PIMH) and the various nitrogen containing compounds (quinoline, carbazole and pyrimidine) were modelled and discussed in the ESI, Section B. † Instrumentation FT-IR spectra (4000-400 cm À1 ) were run on Bruker, Tensor 27 platinum ATR-FTIR spectrometer. The 1 H NMR spectra of ligands and monomer were recorded on a Bruker 400 MHz spectrometer in DMSO-d 6 . Thermogravimetric analyses of imprinted and non-imprinted nanobers were performed using Perkin-Elmer TGA 7 thermogravimetric analyser (TGA). Typically, the samples were heated at a rate of 10 C min À1 under a constant stream of nitrogen gas. The polymer nano-bers were imaged using a TESCAN Vega TS 5136LM scanning electron microscope (SEM). Before images were taken; the various 2-(1H-imidazol-2-yl)-4-phenol nanobers were gold coated to prevent surface charging and to protect the surface material from thermal damage by the electron beam. Nitrogen adsorption/desorption isotherms were measured at 77 K using a TriStar II 3020 3.02 Analyzer by Micromeritics Instrument Corporation to determine surface area and porosity of the nanobers. Prior to each measurement, nanobers were degassed at 60 C for 24 h. The BET surface area, total pore volume and pore size distribution were calculated from these isotherms. Adsorption studies for model compounds was monitored by employing an Agilent 7890A gas chromatograph tted with ame ionization detector (GC-FID). The GC conditions for the adsorption analyses was started with an oven temperature of 50 C ramping to 80 C for 2 min, and then increased to 300 C at a rate of 20 C min À1 , and nally held for 1 min.

FT-IR analysis
The FT-IR spectra of non-imprinted nanobers, carbazoleimprinted nanobers, pyrimidine-imprinted nanobers and quinoline imprinted nanobers are all presented in Fig

Thermogravimetric analysis (TGA) of non-imprinted and imprinted nanobers
A weight loss of loosely-bound solvents within the nanobers were observed at temperatures below 120 C. All nanobers presented a single-step decomposition pattern which occur between 375-450 C.
Non-imprinted nanobers (NIP). NIP nanobers presented a single-step decomposition pattern which occur between 395-440 C. An observed 3% weight loss around 120 C was assigned to loosely-bound (intermolecular) solvent within the nanobers. The decomposition of non-imprinted nanobers backbone only began to occur at temperatures of around 370 C to about 440 C, hence resulting in a total polymer weight loss of 92%, aer which the carbon residue remained. The TGA prole of NIP was presented alongside the proles reported for quinolineimprinted nanobers (QUNMIP), pyrimidine-imprinted nano-bers (PYMMIP) and carbazole-imprinted nanobers (CARMIP) for a better comparison ( Fig. 1-3).
Quinoline-imprinted nanobers (QUNMIP). The quinolineimprinted nanobers gave similar decomposition patterns as likened with NIP nanobers (one step decomposition: 386-440 C). A 4% weight loss observed at around 110 C was attributed to loosely-held (intermolecular) solvent molecules within the nanobers. Followed by a rapid decomposition of quinolineimprinted polymer backbone at 370 C to a temperature of about 450 C (Fig. 1). A total weight loss of 95% was observed.
Pyrimidine-imprinted nanobers (PYMMIP). The pyrimidineimprinted nanobers (PYMMIP) nanobers presented a distinct weight loss between 380 and 430 C. Pyrimidine-imprinted nanobers displayed high stability to around 300 C, this conrmed that the nanobers were dry and free of solvents. Gradual breakdown of polymer backbone only began to occur at temperatures between 390 and 430 C, with a total weight loss of 96% (Fig. 2).
Carbazole-imprinted nanobers (CARMIP). The carbazoleimprinted nanobers (CARMIP) presented one distinct weight losses at around 390 C and 430 C. A 2% weight loss observed at around 110 C was attributed to loosely-bound solvent within the nanobers. Followed by a rapid decomposition of quinolineimprinted polymer backbone at 370 C to a temperature of about 450 C (Fig. 3). A total weight loss of 94% was observed.
The thermal stabilities of molecularly imprinted nanobers obtained via TGA analysis are in the order of; pyrimidineimprinted nanober > carbazole-imprinted nanobers > quinoline imprinted nanobers.

Scanning electron micrograph (SEM) and energy dispersive spectroscopy (EDS) of non-imprinted and imprinted nanobers
The SEM micrographs of non-imprinted and imprinted nano-bers aer washing and drying are presented in Fig. 4A-D. A diameter range of between 100-270 nm was observed for all nanobers (Fig. 4A-D). SEM images also indicated a break in the ber strand of pyrimidine-imprinted nanobers (PYMMIP), this may probably be due to the imprinting effect.
Energy Dispersive Spectroscopy (EDS) images for the various non-imprinted and imprinted nanobers aer washing and drying are presented in Fig. S3. † Chemical characterization of  nanobers aer template removal were determined, it is worth noting that EDS presents qualitative data and therefore cannot be employed as quantitative data. EDS study conrmed that the chemical integrity of the nanobers was preserved even aer washing the templates off the nanobers.

BET surface area
A Brunauer-Emmett-Teller (BET) model was used to calculate the specic surface area and a Barrett-Joyner-Halenda (BJH) model was used to calculate the pore volume distribution and the average pore size of (A) non-imprinted nanobers, (B) quinoline-imprinted nanobers (QUNMIP), (C) pyrimidineimprinted nanobers (PYMMIP) and (D) carbazole-imprinted nanobers (CARMIP).
A decrease in the surface area of the nanobers upon imprinting was due to pores being created by organonitrogen  This journal is © The Royal Society of Chemistry 2018 compounds as seen in the reported pore sizes ( Table 1). The result also displayed changes in nanobers pore sizes (Å), thus corresponding to the sizes of imprinted compounds. The random brous mesh obtained as shown in Fig. 4 may have inuenced the pore size values obtained as no visible pores were seen on the SEM images of the nanobers. Hence, the various pores sizes obtained may be the determined external pores.

Adsorption studies
Nitrogen containing compounds selectivity studies. Adsorption assays were carried out to evaluate the loading capacity and selectivity of imprinted poly 2-(1H-imidazol-2-yl)-4-phenol (PIMH) nanobers. 50 mg of the imprinted adsorbents were added to vials and mixed with 3 mL solution mixture of nitrogen containing compounds (quinoline, carbazole and pyrimidine), dibenzothiophene and naphthalene (120 mg L À1 each).
The corresponding adsorption assays were rst carried out by employing non-imprinted nanobers followed by using imprinted nanobers. The suspension was le under mechanical agitation at 150 rpm for 12 h as described in the adsorption studies (Fig. S4 †). The use of non-imprinted gave a maximum adsorption of 0.62 mg g À1 , 0.51 mg g À1 and 0.63 mg g À1 respectively for quinoline, carbazole and pyrimidine.
Relatively moderate adsorption capacities with no selectivity were observed for non-imprinted when NIP nanobers were employed. However, high adsorption capacities were observed when molecularly imprinted nanobers were employed to target specic N-compounds: (i) quinoline-imprinted nano-bers (QUNMIP) presented 11.7 AE 0.9 mg g À1 , quinoline (Fig. S5 †) (ii) pyrimidine-imprinted nanobers (PYMMIP) presented 11.9 AE 0.8 mg g À1 , pyrimidine (Fig. S6 †) and (iii) carbazole-imprinted nanobers (CARMIP) presented 11.3 AE 1.1 mg g À1 , carbazole (Fig. S7 †). The molecularly imprinted nanobers presented a much higher adsorption capacity as compared to the data observed when molecularly imprinted polybenzimidazole (PBI) was employed, an adsorption capacity of 4.8 mg g À1 was observed with PBI. 17 The non-specic binding nature on non-imprinted nano-bers gave rise to the non-selective adsorption reported as compared to the imprinted nanobers whose binding sites alongside cavities created via imprinting allows for selective adsorption. 26 A reduction of <20 mg L À1 observed for dibenzothiophene and naphthalene was attributed to the chemical properties as well as the high surface area presented by the polymer nanobers. The reduction dibenzothiophene and naphthalene concentrations could have resulted from p-p stacking between absorbent and adsorbates (dibenzothiophene and naphthalene).
Theoretical calculation via subtraction of the unabsorbed Ncompounds indicated that concentrations of 118.8, 117.3 and 116.4 mg L À1 for pyrimidine, quinoline and carbazole, respectively, are required for complete adsorption.

Imprinting factor (k)
The imprinting constant (k) is dened as the ratio of the adsorption capacity of imprinted nanobers (Q MIP ) to the adsorption capacity of the non-imprinted nanobers (Q NIP ). The higher the value of k, the better is the imprinting effect. where k is the imprinting factor, Q NIP (mg g À1 ) is the adsorption capacity of the non-imprinted nanobers and Q MIP (mg g À1 ) is the adsorption capacity of imprinted nanobers. The imprinting factor (k) values for quinoline-imprinted nanobers is 18.92, pyrimidine-imprinted nanobers is 18.56, and carbazole-imprinted nanobers is 22.16, respectively (Table S1 †).

Adsorption kinetics
Adsorption kinetic studies using molecularly imprinted nano-bers showed that nitrogen molecule adsorption was initially fast due to the availability of surface adsorption and thereaer adsorption rate slowed as surface saturation is reached, thus, limiting further nitrogen molecules penetration (Fig. S4 †).
The kinetic mechanism that controls the adsorption process under batch study was monitored by using pseudo-rst-order model (eqn (2)) and pseudo-second-order model (eqn (3)). In pseudo-rst-order model the occupation rate of the adsorption sites is proportional to the number of unoccupied sites, while the pseudo-second-order assumes that adsorption takes place via a chemical reaction process i.e. chemisorption process. Kinetic studies were carried out by using molecularly imprinted nanobers (50 mg) contained in 3 mL of 120 mg L À1 Ncompounds solution.
logðq e À q t Þ ¼ log q e À K 1 2:303 t (2) where q e and q t (mg g À1 ) are the amounts of N-compounds adsorbed on the adsorbent at equilibrium and time t, respectively. K 1 (h À1 ) is the pseudo-rst-order adsorption rate constant and was calculated by plotting the log(q e À q t ) versus t (Fig. 5).
The pseudo-rst-order and pseudo-second-order parameters (coefficients) are presented in Table 2. Based on the obtained correlation coefficients (R 2 ), carbazole, quinoline and pyrimidine tted the pseudo-rst-order model. The pseudosecond-order plot is presented in Fig. S8. †

Adsorption isotherms
The adsorption behaviour of nitrogen containing compounds on imprinted nanobers was followed using the Langmuir and Freundlich isothermal equations (eqn (4) and (5)).
where q e (mg g À1 ) and C e (mg g À1 ) are the amount adsorbed at equilibrium and the equilibrium concentration, (Q m ), is the theoretical maximum adsorption capacity at monolayer (mg g À1 ), and K d is the Langmuir constant (related to the affinity of adsorption sites). 26 Freundlich constants k and n indicating adsorption capacity and intensity respectively were determined from the linear plot of log q e against log C e . Freundlich isotherm indicated a multiple layered adsorption on adsorbents, which may possibly infer nitrogen compound-nitrogen compound interactions on the adsorbent. While Langmuir equation obtained from a plot of C e /q e against C e is probably proof of chemical adsorption, which may usually mean monolayer adsorption on the surface of adsorbents. 26 From the plots, Freundlich adsorption equation tted better (larger correlation coefficient R 2 , Fig. 6 and Table 3) with equilibrium data as compared to the Langmuir parameters and we also observed that Freundlich constant 'n' value lies within the range 1 to 10, thus indicating that adsorption on the nanobers are favourable. 26 The Langmuir parameters plot is presented in Fig. S9. †

Thermodynamic studies
Van't Hoff plot. Fig. 7 shows the Van't Hoff's plot for carbazole, quinoline and pyrimidine adsorptions and the calculated thermodynamic values (DH , DS and DG ad ) for Ncompounds are shown in Table 4. Negative DG ad observed on all interactions indicated feasibility and spontaneity of the adsorption processes. 25 The negative DH values observed for all nitrogen containing compounds pyrimidine, carbazole and quinoline conrmed the exothermic nature of the overallsorption process. The positive value of DS observed for all nitrogen containing compounds suggests increased randomness at the solid/solution interface with some structural changes (in the adsorbate and adsorbent) as well as the binding affinity of the various nitrogen containing compounds to the imprinted nanobers.
The result obtained from Van't Hoff plot is in agreement with the data obtained through DFT studies and isothermal titration calorimetry (ITC) (please see Section B of the ESI †). Briey, DFT studies revealed that hydrogen bond interactions may take place between the lone-pair nitrogen atom of N-compounds

Continuous ow adsorption studies
Continuous ow adsorption technique was employed for the adsorption of pyrimidine, quinoline and carbazole compounds. Breakthrough volumes were evaluated, as they represent the evolution of the concentration of a solution as a function of parameters such as contact time between liquid and solid phase, solvent concentration and temperature. 50 mg of molecularly imprinted nanobers were packed into a cylindrical tube attached to the tip of a syringe containing 5 mL of respective N-compounds. The molecularly imprinted nano-bers were easily contained in the tube without leaving much space and the packing was tightened by conditioning the material with solvent at 0.5 mL h À1 . Adsorption progressed as respective N-compounds ow through the conditioned sorbent. From the adsorption curve, the maximum amount of nitrogen containing compounds retained falls within the range of 0.9-1.5 mL (900-1500 mL). The breakthrough curves of the N-compounds solutions obtained are presented in Fig. 8. C o was the initial concentration (g L À1 ) of the nitrogen compounds and C e was the eluted concentration of the nitrogen compounds. The linear capacity of the column (n s ), the capacity factor of the solute (k) and percentage recovery (r) are calculated from eqn (6)- (8). 22,26 and presented in Table 5.
where V o is the initial volume of the analyte (nitrogen solutions), breakthrough volume (V B ), retention volume (V R ) and hold-up volume (V M ) of the analyte (nitrogen solutions). A recovery rate in the order of pyrimidine > quinoline > carbazole was observed for the continuous ow study.

Adsorbents reusability studies
Reusability studies on the imprinted nanobers were carried out using solid phase extraction (SPE) technique. 27 Solid phase extraction (SPE) is an increasingly useful sample preparation technique. The rebinding adsorption capacities of imprinted nanobers decreased signicantly for all nitrogen compounds as we move from 1st adsorption cycle to the 3rd cycle for carbazole (Fig. S10 †), quinoline (Fig. S11 †) and pyrimidine (Fig. S12 †). This reduction in adsorption capacities upon employing the nanobers for several cycles indicated that the imprinting integrity may have been compromised. 26 Table 6 presented the various concentrations absorbed aer each cycle. GC-FID chromatograms of model fuel before and aer adsorption with molecularly imprinted nanober is presented in Fig. S13. †
Adsorption studies for the removal of organonitrogen compounds was carried out by weighing 150 mg of imprinted nanobers (comprising of 50 mg quinoline-imprinted, 50 mg carbazole-imprinted and 50 mg pyrimidine-imprinted nano-bers) as adsorbent. Adsorption proceeded under SPE manifold by conditioning imprinted nanobers at a vacuum pressure of 20 in Hg with a solution of hexane followed by loading the hydrotreated diesel (1 mL hydrotreated diesel in 2 mL of hexane). Cyclohexane was employed to wash interfering molecules from the sorbent and nally N-compounds were eluted by using a mixture of acetonitrile : methanol (1 : 1).
GC Â GC-high-resolution TOF-MS surface plot conrmed a reduction in the presence of alkylated organonitrogen compounds in the hydrotreated fuel (Fig. 9). According to the MS data some of the identied alkylated organonitrogen compounds peak area reduced aer adsorption studies (Table 7).  As observed in Table 7, imprinted nanobers show promise owing to its high surface area and chemical characteristics, thus, enabling the adsorption of refractory organonitrogen compounds. Though, some complexities were observed as the adsorbent also wiped out some non-imprinted compounds. The ability of the polymer nanobers to adsorb these compounds was attributed to possible hydrogen bonding interactions between adsorbent and these compounds, 1-phenyl-1propanamine and 4-pentyloxyaniline and 2-butyl-1-pyrroline (Table 7), which could easily interact via hydrogen bond formation with the polymer nanobers. Imprinted nanobers was unable to eliminate 3-(N,N-dimethylamino)-9methylcarbazole completely due to the highly alkylated nature of the compound, thus, inhibiting interactions with the active sites of the adsorbent.
Many solid adsorbents have been employed for denitrogenation of fuels and these adsorbents have proven to be worthwhile in terms of general performance. The use of imprinted nanobers is relatively new and limited literature exists. However, several investigations of ADN using solid sorbents such as MOFs have been reported. 28,29 They observed that MOFs with high porosity absorbed higher concentrations of nitrogen containing compounds (NCCs). [29][30][31] A study reported by Nuzhdin et al. 29 indicated that a total of 1.3 mmol of nitrogen containing compounds (NCCs) was removed by 1 g of MIL-101(Cr). Results obtained with the use of molecularly imprinted nano-bers in this study could be said to be comparable with the results reported by Nuzhdin et al. 29 and some others reported in the literature. 29 The use of poly 1,1 0 -binaphthyl-2,2 0 -diol nano-bers for the adsorption of quinoline and isoquinoline in a model simulated fuel presented an adsorption capacity of 2.2  a NB: Initial concentration ¼ 120 mg L À1 . and 2.4 mg g À1 , respectively. 32 These capacities falls short of the value reported in the current study, hence, conrming an improvement in the fabricated material through imprinting process. Therefore, the use of molecularly imprinted nanobers as adsorbent in the adsorption of NCCs offers improved surface area, porosity (cavities), adsorption capacities and selectivity. 31 Theoretical studies The atomic level interaction of the various nitrogen containing compounds (quinoline, carbazole and pyrimidine) with poly 2-(1H-imidazol-2-yl)-4-phenol were predicted by molecular interaction studies using B3LYP functional with a basis set 6-311G++(d,p) using the Gaussian09 soware (calculated at 298 K) under tight convergence criteria. 33  Upon interacting with N-compounds (quinoline, pyrimidine and carbazole), HOMO position of the adducts originates from 2-(1H-imidazol-2-yl)-4-phenol, while LUMO centers mostly around each nitrogen containing compounds (Fig. 10-12). This    (Table S2 †). According to hard and so acids bases (HSAB), hard acids interact more strongly with hard bases, while so acids interact more strongly with so bases. 28 The order of N-compound hardness and soness is pyrimidine (PYM) < quinoline (QUN) < carbazole (CAR), thus, indicating that pyrimidine is more reactive and carbazole is least reactive. Molecules with large electronegativity can be considered as stronger electron acceptors. 34 Electronegativity data agrees with the HOMO-LUMO diagram which indicates that electrons are donated by 2-(1H-imidazol-2-yl)-4phenol (PIMH) and accepted N-compounds (quinoline, pyrimidine and carbazole). Some electronic structure identiers of the studied adducts are presented in Table 8.

Conclusions
Molecular imprinting on 2-(1H-imidazol-2-yl)-4-phenol enhanced adsorption capacities and selectivity for individual nitrogen compounds due to their specic binding nature and high adsorption capacities are described. A better regression R 2 presented by Freundlich isotherm conrmed multilayer adsorption attributed to the interactions between imprinted nanobers and nitrogen compounds, and possibly between nitrogen molecules. The nanobers displayed excellent adsorption properties when employed under SPE conditions to explore hydrophobic interactions (van der Waals or dispersion forces) and hydrophilic interactions (hydrogen bonding, pi-pi interactions, dipole-dipole interactions). Thermodynamic parameters obtained from isothermal titration calorimetry (ITC) revealed that quinoline-PIMH and pyrimidine-PIMH interactions are exothermic in nature, while carbazole-PIMH is endothermic in nature. Molecular modelling also conrmed that 2-(1H-imidazol-2-yl)-4-phenol indicated that hydrogen bond interactions may take place between the lone-pair nitrogen atom of N-compounds (quinoline and pyrimidine) and the -OH, -NH groups of the PIMH nanobers. Carbazole on the other hand offers weak interactions. Further DFT also conrmed the feasibility of p-p interactions between the imidazole rings and the aromatic N-compounds. The complex nature of N-compounds in fuel complicate the structure/function approach on MIPs for targeting these unwanted compounds.

Conflicts of interest
There are no conicts to declare.