Show page "loading"

I have a SPA-type system that uses adminlte .css, in one method I load several SQL selects to create a page with several tabs of information. I would like to show a loading before assembling the page. I created a simple page to be set up before calling MODELS. But the page is not shown before, it is only shown after SELECT-SQL processing.

PHP Code:

public function trazer_alunosdaturma($ncodtur=null) {
//I tried to put it here
        //$this->load->view('includes/html_header');
       //$this->load->view('includes/menupermissoesadmlte');
       //$this->load->view('v_notasturmax',$dados);
       //$this->load->view('loading');
       //$this->load->view('includes/html_footer');  
  
        $this->load->model('Notasturma_model','notasturma');    
        $dados["notasturma"] = $this->notasturma->getfetchalunosdaturma($ncodtur); 
        $dados["disciplinasturma"] = $this->notasturma->getfetchdisciplinasdaturma($ncodtur);
        $dados["professorturma"]=$this->notasturma->getfetchprofessoresdaturma($ncodtur);
        $dados["professores"]=$this->prof->getallprof();
        $retornoinsert=$this->notasturma->montarlistaalunosmapao($ncodtur);
        if ($retornoinsert=0)
        {
            // erro , preciso resolver mensagem de erro e não ir a frente
        }else{
          
            $dados['mapao']=$this->notasturma->abastecertbmapao($ncodtur);
            $this->load->view('includes/html_header');
            $this->load->view('includes/menupermissoesadmlte');
            $this->load->view('v_visaodaturma',$dados);
            $this->load->view('includes/html_footer');    
        };
        
        
    }