Acetaminophen and mepirizole molecular adsorption studies on novel ζ – phosphorene nanotube based on first-principles investigation

ABSTRACT Based on the first-principles investigation, we explored the adsorption properties of two drug molecules on ζ – phosphorene nanotube (ζ-PNT) present in the aqueous environment. Firstly, the structural stableness of ζ-PNT is ensured with the support of formation energy (−5.005 eV/atom). Additionally, the electronic properties of ζ-PNT are studied by band structure and projected density of states (PDOS) spectrum. The energy band gap of ζ-PNT is found to be 1.298 eV, which confirms the semiconductor nature of the base substrate. The ζ-PNT is used as the base substrate to adsorb acetaminophen and mepirizole drug molecules in the contaminated water. The adsorption energy of ζ-PNT owing to molecular adsorption of drug molecules figures out to be in the chemisorption regime (−4.244 eV to −9.058 eV). Besides, the variation in the energy band, charge transfer, band structure, and electron density difference studies due to acetaminophen and mepirizole adsorption on ζ-PNT is reported. The outcome reveals that ζ-PNT is a possible material for acetaminophen and mepirizole removal from the contaminated water.


Introduction
The drug acetaminophen is recognised by U.S. Food and Drug Administration (FDA) and health authorities worldwide as an effective antipyretic and analgesic drug [1]. Acetaminophen is used to treat toothaches, backaches, osteoarthritis, headaches, menstrual periods, cold & flu aches, and pains. Also, the health hazard of acetaminophen includes aplastic anaemia, swollen tongue, central nervous system stimulation, skin eruptions, convulsions, excitement, delirium, rapid pulse, and vascular collapse [2]. Moreover, the human body excretes 58-68% of consumed acetaminophen. The low adsorption rate of drug acetaminophen and high rate of consumption along with high water solubility leads to wastewater contamination [3]. Acetaminophen reaches the aquatic environment through urine, direct disposal of drugs, faeces, and hospital effluents. Verlicchi et al. reported that acetaminophen is present in wastewater in the range of 0.5-1.2 ppb before treatment and 0.012-0.058 ppb after treating the wastewater in the aquatic environment [4]. H. N. Phong Vo et al. studied the monitoring and removal of acetaminophen from contaminated water released from hospital wastewater using peroxidase enzymes [5]. R. Naresh Kumar group [6] explored the removal of acetaminophen from river water by electrocoagulation by deploying aluminum-aluminum electrodes, which have a 2 cm interelectrode distance with a potential of 9 V. V. K. Vaidyanathan team [7] removed acetaminophen with the help of silica microspheres from wastewater. The carcinogenic hazard nature of acetaminophen was reported by Jay E. Sirois [8]. The report presents information on human epidemiology, genotoxicity, preclinical carcinogenicity, and mechanistic studies examining biochemical pathways of acetaminophen metabolism. M. Negarestani et al. [9] studied the removal of ibuprofen and acetaminophen using electrocoagulation from underground water. Raj Mohan Balakrishnan et al. [10] adsorbed ibuprofen, streptomycin, and acetaminophen using amine functionalised superparamagnetic silica nanocomposite. Graphene modified with GdTiO 3 perovskite composite is used for sensing dopamine and acetaminophen [11].
Mepirizole also called epirizole is an anti-inflammatory agent, which has antipyretic, analgesic, and platelet-inhibitory actions. The health hazard of mepirizole, includes respiratory tract irritation, serious eye irritation /eye damage, and skin irritation/corrosion [12]. H. Tanaka et al. [13] reported the pathogenic mechanism related to mepirizole induced duodenal damage in rats. I. Japundzic et al. [14] reported the influence of duodenal ulcerogenic mepirizole on the liver and small intestinal activity in rats.
In recent years, the advancement of two-dimension (2D) materials technology further advanced from graphene to monolayer group 15 flakes [15][16][17][18][19][20]. Moreover, phosphorene is one among group 15 nanoflakes widely used in nano-photonic drugs, energy materials, optoelectronic, chemical, and biosensors [21,22]. The 2D phosphorene leads to changes in the electron motion confinement, band structure change, and changes in mechanical, optical, and electronic properties [23][24][25][26]. D. C. Arriagada et al. [27] reported phosphorene-fullerene nanostructures, which shows the modulation in electronic properties based on the fullerene size. M.R. Benam et al. [28] studied the detection of aspartic acid, alanine, and glycine amino acids with the phosphorene nanosheet. The maximum sensing response of 59.3% is obtained for aspartic acid. Binbin Zhang et al. [29] used fibrous red phosphorene as a gas sensing element toward O 3 , SO 2 NO, and NO 2 molecules. The sensing response is increased for NO upon applying external in-plane strain. Ping Wu group [30] studied the adsorption behaviour of volatile organic compounds (VOCs), namely benzene, toluene, m-xylene, o-xylene, p-xylene, and formaldehyde on fibrous red phosphorene. The report reveals that based on the uniaxial and biaxial strains the sensing performance of VOCs gets enhanced. Chaoyu He et al. [31] reported five new allotropes of low-energy phosphorene obtained based on the combination of gene segments. Recently, many researchers focused on the various properties of phosphorene nanotubes and their potential applications. Douxing Pan et al. [32] have reported the electronic properties of phosphorous nanotube and fine-tuned the band gap by changing the chiral vector, which is of great interest in the application of semiconductor devices. Lin Ju et al. [33] have computationally built the blue phosphorene nanotube and studied the variation in electronic properties by applying strain and changing the diameter of the tube. Moreover, the authors suggested that the blue phosphorene nanotube is a good candidate for the application of water-splitting photocatalyst. Corrrea group [34] studied the electronic properties of blue phosphorene nanotube for both armchair and zigzag forms. The study revealed that the electronic properties can be tailored by creating vacancy, which is much useful to develop novel optoelectronic devices. Menghao Wu et al. [35] predicted nine non-honeycomb structures of phosphorene polymorphs. Moreover, concerning the reported work of Menghao Wu et al. [35], we constructed ζphosphorene nanotube and used it as a base material to adsorb acetaminophen and mepirizole drugs in the proposed work.

Computational specifications
The quantum ATK package [36] is utilised to study the geometric stableness and electronic attributes of ζphosphorene nanotube (ζ-PNT) in the framework of density functional theory (DFT). The adsorption attributes of acetaminophen and mepirizole drug molecules on ζ-PNT are studied with the help of Generalised Gradient Approximation (GGA) with Becke86 -Lee -Yang-Parr (B86LYP) exchange-correlation functional level of theory [37,38]. Since the proposed work deals with the adsorption aspects of acetaminophen and mepirizole, we employed Grimme's DFT-D3 method to integrate the influence of van der Waals interaction [39]. Besides, the double zeta polarisation basis set is involved in the proposed work and the Hellmann-Feynman force during the calculation is kept at 0.002 eV/Å. The energy convergence between the adjacent steps is preserved at 10 −6 eV with the energy cut-off kept in the range of 500 eV. The Brillouin zones at the Monkhorst-Pack grid of 1 × 1×25 is utilised during the calculation. In order to eliminate the field effects among the successive layers, vacuum space is set to 16 Å.

ζphosphorene nanotube structural studies and electronic properties
The non-honeycomb polymorphs of phosphorene nanosheets are first constructed and with the help of the tube wrapper tool in ATK-VNL, ζ-PNT is built. The space group of ζphosphorene is P-1 (No.2). The fully optimised lattice parameter of ζphosphorene is noticed to be a = 6.44 Å, b = 5.32 Å. Typically, the ζphosphorene has a different bond distance between Patoms with a figure of 2.23 and 2.31 Å. The calculated lattice parameters are in consistent with previous computational work [35]. The top and side view of ζ-PNT is depicted in Figure 1.
In order to ensure the geometric stableness of ζ-PNT, the formation energy E form is calculated based on the below relation [40][41][42], herein, E(z − PNT) denotes the energy of pristine ζ-PNT,   E(P) denotes the energy of bare phosphorous, and 'n' refers to the number of phosphorous atoms in ζ-PNT. Besides, the calculated value of E form for ζ-PNT is observed to be −5.005 eV/ atom, where the negative magnitude indicates the stable geometry of ζ-PNT. Furthermore, to verify the dynamical stability of ζ-PNT, the phonon band spectrum is plotted and displayed in Figure 1(b). From the phonon band graph, it is clearly revealed that there is no negative (imaginary) frequencies are noticed, which confirmed the dynamical stability of the base ζ-PNT substrate. Owing to the confirmation of dynamical stability, researchers can synthesis the base material experimentally with the support of a suitable synthesising technique.
The electronic properties such as band structure and projected density of states (PDOS) give the perceptions of the applicability of ζ-PNT as a base substrate to adsorb acetaminophen and mepirizole molecules [43][44][45][46]. Figure 2 denotes the band structure and PDOS spectrum of ζ-PNT. The band structure reveals the energy band gap of ζ-PNT along the gamma point, which is calculated to be 1.298 eV in its pristine form. The PDOS spectrum indicates the support of each orbital towards the total DOS (TDOS). Moreover, the p-orbital of phosphorous atoms supports significantly to TDOS spectrum. Furthermore, peaks are noticed beyond 1 eV in the conduction band of ζ-PNT, which strengthen that ζ-PNT can be used as adsorbing medium in the aqueous medium having acetaminophen and mepirizole drug molecules.

Acetaminophen and mepirizole drug adsorption studies on ζphosphorene nanotube
The adsorption of acetaminophen and mepirizole drug molecules in the aqueous medium on ζ-PNT is studied in the proposed work. Moreover, before studying the adsorption of drug molecules, the prominent energy minima sites are identified with reference to other possible configurations of adsorption. Only for the discussed sites, the energy minima (global minima) are obtained. In the beginning, we name the adsorption sites, the adsorption of acetaminophen drug molecule on ζ-PNT along the inner, parallel, and vertical valley positions are named as orientation AM1, AM2, and AM3, respectively as shown in Figure 3(a). Similarly, the adsorption of mepirizole on inner, parallel, and vertical valley sites are called orientation MZ1, MZ2, and MZ3 correspondingly as displayed in Figure 3(b). Table 1 gives the information with regard to charge transfer, adsorption energy, and band gap variation with regard to the different orientations. The adsorption energy E ad due to adsorption of acetaminophen and mepirizole molecules on ζ-PNT is computed based on the below expression [47][48][49][50][51][52][53][54], Where E(complex) is the energy of ζ-PNT with drug molecules, E(acetaminophen or mepirizole) denotes the energy of acetaminophen or mepirizole molecules, E(z − PNT) refers to the energy of bare ζ-PNT, E(H 2 O) is the energy of water molecule and BSSE is the basis set superposition energy to eradicate the overlapping effects in the basis set [55].
Besides, E ad is observed as −4.244, −6.022, −6.424, −9.058, −6.978, and −5.066 eV for the orientation AM1, AM2, AM3, MZ1, MZ2 and MZ3, respectively. The E ad indicates that the drug molecules acetaminophen and mepirizole are chemisorbed on ζ-PNT, which is governed by the higher value of E ad . Also, it is evident that the adsorption of acetaminophen and mepirizole on ζ-PNT is exothermic, which favours the adsorption of drug molecules in the contaminated water. The main concentration of the present study is to explore the interaction behaviour of ζ-PNT to water pollutants in the aqueous medium. Therefore, we investigated the effect of the water molecule (H 2 O) upon the interaction of chief water pollutants on ζ-PNT. The adsorption energy of ζ-PNT upon the adsorption of a water molecule is noticed to be −0.225 eV, which is relatively lower than the adsorption energy of chief molecules adsorbed ζ-PNT. The charge transfer (DQ) plays an important role to decide whether the drug molecules acetaminophen and mepirizole upon adsorption on ζ-PNT acts as Figure 4 Continued acceptor or donors [56][57][58][59][60][61][62]. Moreover, 0.044, 0.229, 0.121, 0.473, 0.198, and 0.153 e are noticed due to adsorption of acetaminophen and mepirizole on ζ-PNT. The positive value of DQ strongly denotes the donor behaviour of drug molecules and ζ-PNT is the acceptor of electrons. We calculated the changes in the energy gap variation using the following relation [63][64][65][66], Where E g(isolated) and E g(complex) refers to the energy gap of pristine and chief molecule adsorbed ζ-PNT correspondingly. The adsorption of acetaminophen and mepirizole on ζ-PNT changes the energy band gap, which arose due to the orbital hybridisation of drug molecules with ζ-PNT. Besides, the changes in the E a g are recorded as 30.59, 52.85, 10.17, 100, 35.21, and 2.16% for orientations AM1, AM2, AM3, MZ1, MZ2, and MZ3 correspondingly. A strong adsorption leads to drastic change in E a g variation due to acetaminophen and mepirizole on ζ-PNT. 3.3. Density of states and band structure analysis of ζphosphorene nanotube due to Acetaminophen and mepirizole drug adsorption The changes in the electronic properties of ζ-PNT are discussed in terms of PDOS and band structure analysis due to the adsorption of acetaminophen and mepirizole drugs [67][68][69]. Figure 4(a-f) depicts the band structure and PDOS spectrum of ζ-PNT for the orientations AM1, AM2, AM3, MZ1, MZ2, and MZ3, respectively. A band gap of 1.298 eV is observed for isolated ζ-PNT. However, in the presence of a water environment the energy band gap of ζ-PNT changes to 1.278 eV. Besides, the changes in the band gap of ζ-PNT are recorded as 0.901, 0.612, 1.166, 0, 0.841, and 1.270 eV respectively is noticed along the gamma point in the band structure diagram for the orientation AM1, AM2, AM3, MZ1, MZ2, and MZ3. Also, the shift in the peaks is observed in the conduction band as well as in the valence band owing to the adsorption of drug molecules on ζ-PNT depicted in the  PDOS spectrums. The total DOS resembles mostly with regard to p-orbital of PDOS, which is influenced by the orbital hybridisation of target acetaminophen and mepirizole molecules with ζ-PNT.
The electron density difference diagram (EDD) throws the lights on the donor or acceptor nature and changes in the electronic properties of ζ-PNT due to molecular adsorption of acetaminophen and mepirizole drugs [70][71][72][73][74][75]. Figure 5(a) depicts the electron density diagram of pristine ζ-PNT. The blue and red colour shows electron depletion and electron accumulation, respectively. Moreover, the adsorption of acetaminophen and mepirizole molecules on ζ-PNT shows that electrons are transferred from drug molecules to ζ-PNT as observed from the EDD diagram as depicted in Figure 5(b,  c). Also, the transferal of electrons from drug molecules to ζ-PNT is in agreement with the results of charge transfer (DQ). Figure 6 depicts the insights into the chemisorption aspects of acetaminophen and mepirizole molecules on ζ-PNT. Thus, it is evident from the EDD, band structure, and PDOS spectrum that the electronic attributes of ζ-PNT change with regard to adsorption of acetaminophen and mepirizole molecules in the water environment.

Finishing notes
We investigated the structural stableness and dynamical stability of ζ-PNT using formation energy and phonon band maps. Using band structure and PDOS spectrum, the electronic features of ζ-PNT are examined. The calculated band gap of ζ-PNT is 1.298 eV (GGA/B86LYP level of theory), which confirms the semiconductor nature of the base substrate. The ζ-PNT is deployed as adsorbing substrate for acetaminophen and mepirizole drug molecules in the aqueous environment. The adsorption energy falls in the range of −4.244 to −9.058 eV supporting the chemisorption of drug molecules. The variation of the band gap, charge transfer, peak shift in the PDOS spectrum, and electron density difference confirms the adsorption of drug molecules on ζ-PNT. Lastly, the findings of the work support the employment of ζ-PNT as a new material for the removal of acetaminophen and mepirizole in polluted water. The future perspective opens the gate for new material ζ-PNT as a substitute for silica microspheres and other enzymes for the removal of acetaminophen and mepirizole molecules.